HTTP API — Pay-as-you-go (Session)#

A streaming payment channel built on an on-chain Escrow contract. The Buyer opens the channel and deposits funds; the Seller accumulates consumption via off-chain EIP-712 Vouchers; the channel finally settles on-chain and refunds the unused balance.

Base URL: https://web3.okx.com
Path prefix: /api/v6/pay/mpp/session
Network: X Layer (chainId 196)

Authentication#

All endpoints require API Key authentication. The following headers must be provided:

Header	Required	Description
`OK-ACCESS-KEY`	Yes	API Key
`OK-ACCESS-SIGN`	Yes	Request signature
`OK-ACCESS-PASSPHRASE`	Yes	API passphrase
`OK-ACCESS-TIMESTAMP`	Yes	ISO 8601 timestamp
`Content-Type`	Yes	`application/json` for POST requests

All responses use a unified envelope:

json

{
  "code": "0",
  "msg": "success",
  "data": { /* business fields */ }
}

On business errors, code is non-"0" and data is null. See the Error codes section at the end of this page.

1. /api/v6/pay/mpp/session/open#

POST

/api/v6/pay/mpp/session/open

Open a payment channel. Two modes are supported:

transaction mode: server-side opens — the Buyer provides an EIP-3009 authorization, and the Broker submits the on-chain openChannel transaction on their behalf
hash mode: the client opens the channel themselves and provides the broadcast transaction hash for the Broker to verify

Request parameters#

Parameter	Type	Required	Description
`challenge`	`Object`	Yes	The Challenge object issued by the server (echo back as-is). See Challenge
`payload`	`Object`	Yes	Payment receipt
`payload.action`	`String`	Yes	Always `"open"`
`payload.type`	`String`	Yes	`"transaction"` (server-side opens) or `"hash"` (client-side already opened)
`payload.channelId`	`String`	Yes	Channel ID (bytes32, client-precomputed)
`payload.authorization`	`Object`	Conditional	Required when type=`"transaction"`; the EIP-3009 authorization object
`payload.authorization.type`	`String`	Conditional	Always `"eip-3009"`
`payload.authorization.from`	`String`	Conditional	Payer address
`payload.authorization.to`	`String`	Conditional	Escrow contract address
`payload.authorization.value`	`String`	Conditional	Deposit amount (base units)
`payload.authorization.validAfter`	`String`	Conditional	Authorization start Unix timestamp
`payload.authorization.validBefore`	`String`	Conditional	Authorization expiry Unix timestamp
`payload.authorization.nonce`	`String`	Conditional	Random bytes32
`payload.signature`	`String`	Conditional	Required when type=`"transaction"`; EIP-3009 signature (65 bytes)
`payload.hash`	`String`	Conditional	Required when type=`"hash"`; on-chain open transaction hash
`payload.salt`	`String`	Yes	Random bytes32, used to compute channelId
`payload.authorizedSigner`	`String`	No	Delegated signer address; defaults to `0x0000...0000`
`source`	`String`	Conditional	Required when type=`"hash"`; payer DID (`did:pkh:eip155:196:0x...`)

Response parameters#

Parameter	Type	Description
`method`	`String`	Always `"evm"`
`intent`	`String`	Always `"session"`
`status`	`String`	Always `"success"`
`timestamp`	`String`	RFC 3339 response time
`channelId`	`String`	Channel ID (bytes32)
`chainId`	`Integer`	EVM chain ID, e.g. `196`
`reference`	`String`	On-chain transaction hash (returned in transaction mode)
`deposit`	`String`	Currently known on-chain deposit (base units)

Request example — hash mode (client-side opens)#

bash

curl --location --request POST 'https://web3.okx.com/api/v6/pay/mpp/session/open' \
--header 'Content-Type: application/json' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z' \
--data '{
  "challenge": {
    "id": "kM9xPqWvT2nJrHsY4aDfEb",
    "realm": "api.llm-service.com",
    "method": "evm",
    "intent": "session",
    "request": "eyJ...",
    "expires": "2026-04-01T12:05:00Z"
  },
  "source": "did:pkh:eip155:196:0xaabbccddee11223344556677889900aabbccddee",
  "payload": {
    "action": "open",
    "type": "hash",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "hash": "0x9f8e7d6c5b4a39281700abcdef1234567890abcdef1234567890abcdef123456",
    "signature": "0xabcdef1234567890...",
    "authorizedSigner": "0x742d35cc6634c0532925a3b844bc9e7595f8fe00",
    "salt": "0xaaaa1234bbbb5678cccc9012dddd3456eeee7890ffff1234aaaa5678bbbb9012"
  }
}'

Request example — transaction mode (server-side opens)#

bash

curl --location --request POST 'https://web3.okx.com/api/v6/pay/mpp/session/open' \
--header 'Content-Type: application/json' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z' \
--data '{
  "challenge": {
    "id": "kM9xPqWvT2nJrHsY4aDfEb",
    "realm": "api.llm-service.com",
    "method": "evm",
    "intent": "session",
    "request": "eyJ...",
    "expires": "2026-04-01T12:05:00Z"
  },
  "payload": {
    "action": "open",
    "type": "transaction",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "authorization": {
      "type": "eip-3009",
      "from": "0xaabbccddee11223344556677889900aabbccddee",
      "to": "0x1234567890abcdef1234567890abcdef12345678",
      "value": "10000000",
      "validAfter": "0",
      "validBefore": "1743523500",
      "nonce": "0xaaaa1111bbbb2222cccc3333dddd4444eeee5555ffff6666aaaa7777bbbb8888"
    },
    "signature": "0xabcdef...eip3009sig",
    "authorizedSigner": "0x742d35cc6634c0532925a3b844bc9e7595f8fe00",
    "salt": "0xaaaa1234bbbb5678cccc9012dddd3456eeee7890ffff1234aaaa5678bbbb9012"
  }
}'

Response example#

json

{
  "code": "0",
  "msg": "",
  "data": {
    "method": "evm",
    "intent": "session",
    "status": "success",
    "timestamp": "2026-04-01T12:04:30Z",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "chainId": 196,
    "reference": "0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890",
    "deposit": "10000000"
  }
}

2. /api/v6/pay/mpp/session/topUp#

POST

/api/v6/pay/mpp/session/topUp

Top up the deposit on an already-open channel. Supports transaction mode (server-side tops up) and hash mode (client-side already topped up).

Request parameters#

Parameter	Type	Required	Description
`challenge`	`Object`	No	Server-issued Challenge object. See Challenge
`payload`	`Object`	Yes	Payment receipt
`payload.action`	`String`	Yes	Always `"topUp"`
`payload.type`	`String`	Yes	`"transaction"` (server-side tops up) or `"hash"` (client-side already topped up)
`payload.channelId`	`String`	Yes	Channel ID (bytes32)
`payload.authorization`	`Object`	Conditional	Required when type=`"transaction"`; EIP-3009 authorization object
`payload.authorization.type`	`String`	Conditional	Always `"eip-3009"`
`payload.authorization.from`	`String`	Conditional	Payer address
`payload.authorization.to`	`String`	Conditional	Escrow contract address
`payload.authorization.value`	`String`	Conditional	Top-up amount (base units)
`payload.authorization.validAfter`	`String`	Conditional	Authorization start Unix timestamp
`payload.authorization.validBefore`	`String`	Conditional	Authorization expiry Unix timestamp
`payload.authorization.nonce`	`String`	Conditional	Random bytes32
`payload.signature`	`String`	Conditional	Required when type=`"transaction"`; EIP-3009 signature (65 bytes)
`payload.hash`	`String`	Conditional	Required when type=`"hash"`; on-chain topUp transaction hash
`payload.additionalDeposit`	`String`	Yes	The amount being added this time (base units)
`payload.topUpSalt`	`String`	Yes	Random bytes32, required for topUp
`source`	`String`	Conditional	Required when type=`"hash"`; payer DID (`did:pkh:eip155:196:0x...`)

Response parameters#

Parameter	Type	Description
`method`	`String`	Always `"evm"`
`intent`	`String`	Always `"session"`
`status`	`String`	Always `"success"`
`timestamp`	`String`	RFC 3339 response time
`channelId`	`String`	Channel ID (bytes32)
`chainId`	`Integer`	EVM chain ID, e.g. `196`
`reference`	`String`	On-chain transaction hash (returned in transaction mode)
`deposit`	`String`	Currently known total on-chain deposit (base units)

Request example — transaction mode (server-side tops up)#

bash

curl --location --request POST 'https://web3.okx.com/api/v6/pay/mpp/session/topUp' \
--header 'Content-Type: application/json' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z' \
--data '{
  "payload": {
    "action": "topUp",
    "type": "transaction",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "authorization": {
      "type": "eip-3009",
      "from": "0xaabbccddee11223344556677889900aabbccddee",
      "to": "0x1234567890abcdef1234567890abcdef12345678",
      "value": "5000000",
      "validAfter": "0",
      "validBefore": "1743523500",
      "nonce": "0xcccc1234dddd5678eeee9012ffff3456aaaa7890bbbb1234cccc5678dddd9012"
    },
    "signature": "0xefgh....",
    "additionalDeposit": "5000000",
    "topUpSalt": "0xdddd1234eeee5678ffff9012aaaa3456bbbb7890cccc1234dddd5678eeee9012"
  }
}'

Request example — hash mode (client-side already topped up)#

bash

curl --location --request POST 'https://web3.okx.com/api/v6/pay/mpp/session/topUp' \
--header 'Content-Type: application/json' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z' \
--data '{
  "challenge": {
    "id": "qB3wErTyU7iOpAsD9fGhJk",
    "realm": "api.llm-service.com",
    "method": "evm",
    "intent": "session",
    "request": "eyJhbW91bnQiOiIxMDAi...",
    "expires": "2026-04-01T12:05:00Z"
  },
  "source": "did:pkh:eip155:196:0xaabbccddee11223344556677889900aabbccddee",
  "payload": {
    "action": "topUp",
    "type": "hash",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "hash": "0x9f8e7d6c5b4a3928170fabcdef1234567890abcdef1234567890abcdef123456",
    "additionalDeposit": "5000000",
    "topUpSalt": "0xdddd1234eeee5678ffff9012aaaa3456bbbb7890cccc1234dddd5678eeee9012"
  }
}'

Response example#

json

{
  "code": "0",
  "msg": "",
  "data": {
    "method": "evm",
    "intent": "session",
    "status": "success",
    "timestamp": "2026-04-01T12:04:30Z",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "chainId": 196,
    "reference": "0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890",
    "deposit": "15000000"
  }
}

3. /api/v6/pay/mpp/session/settle#

POST

/api/v6/pay/mpp/session/settle

Mid-stream settle — the server submits the Voucher on-chain on behalf of the merchant. The merchant (payee) signs an EIP-712 SettleAuthorization with their own key; the Voucher signature (signed by payer or authorizedSigner) is uploaded with the request. The contract calls settleWithAuthorization.

Request parameters#

Parameter	Type	Required	Description
`payload`	`Object`	Yes	Settle payload
`payload.action`	`String`	No	`"settle"`
`payload.channelId`	`String`	Yes	Channel ID (bytes32 hex, 0x-prefixed)
`payload.cumulativeAmount`	`String`	Yes	Cumulative amount to settle (token base units, uint128 decimal string). If `<= settledOnChain` the server short-circuits without going on-chain
`payload.voucherSignature`	`String`	Yes	EIP-712 Voucher signature (65-byte r‖s‖v hex, 0x-prefixed). Signer = `channel.authorizedSigner` (or `channel.payer` if not set)
`payload.payeeSignature`	`String`	Yes	EIP-712 SettleAuthorization signature (65 bytes). Signer = `channel.payee`
`payload.nonce`	`String`	Yes	uint256 decimal string, randomly generated by the merchant. The `(payee, channelId, nonce)` tuple is unique on-chain; reuse is rejected with `NonceAlreadyUsed`
`payload.deadline`	`String`	Yes	Signature expiry Unix seconds. Rejected when current server time > deadline

Response parameters#

Parameter	Type	Description
`method`	`String`	Always `"evm"`
`intent`	`String`	Always `"session"`
`status`	`String`	Always `"success"`
`timestamp`	`String`	RFC 3339 response time
`channelId`	`String`	Channel ID (bytes32)
`chainId`	`Integer`	EVM chain ID, e.g. `196`
`reference`	`String`	On-chain transaction hash
`deposit`	`String`	Currently known on-chain deposit (base units)

Request example#

bash

curl --location --request POST 'https://web3.okx.com/api/v6/pay/mpp/session/settle' \
--header 'Content-Type: application/json' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z' \
--data '{
  "payload": {
    "action": "settle",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "cumulativeAmount": "250000",
    "voucherSignature": "0x4a5b6c7d8e9fa0b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b501",
    "payeeSignature": "0x11223344556677889900aabbccddeeff00112233445566778899aabbccddeeff1b",
    "nonce": "17890324512398000000000000000000000000000000000000000000000000000001",
    "deadline": "1745500000"
  }
}'

Response example#

json

{
  "code": "0",
  "msg": "",
  "data": {
    "method": "evm",
    "intent": "session",
    "status": "success",
    "timestamp": "2026-04-01T12:04:30Z",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "chainId": 196,
    "reference": "0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890",
    "deposit": "10000000"
  }
}

4. /api/v6/pay/mpp/session/close#

POST

/api/v6/pay/mpp/session/close

Close the channel and finalize settlement. Uses max(client amount, server's highest held Voucher) to protect merchant revenue. After settlement, the Escrow contract refunds the unused deposit to the payer.

When cumulativeAmount <= settledOnChain, the waiver branch is taken (no new Voucher signature required).

Request parameters#

Parameter	Type	Required	Description
`payload`	`Object`	Yes	Close payload
`payload.action`	`String`	No	`"close"`
`payload.channelId`	`String`	Yes	Channel ID (bytes32 hex, 0x-prefixed)
`payload.cumulativeAmount`	`String`	Yes	Final cumulative amount (token base units, uint128 decimal string). When `<= settledOnChain` the waiver branch is taken
`payload.voucherSignature`	`String`	Conditional	EIP-712 Voucher signature (65-byte r‖s‖v hex). Required on the normal branch; can be empty `""` on the waiver branch
`payload.payeeSignature`	`String`	Yes	EIP-712 CloseAuthorization signature (65 bytes). Signer = `channel.payee`
`payload.nonce`	`String`	Yes	uint256 decimal string, randomly generated by the merchant. Shares the same `(payee, channelId, nonce)` used-set with SettleAuthorization — cannot be reused across types
`payload.deadline`	`String`	Yes	Signature expiry Unix seconds. Rejected when current server time > deadline

Response parameters#

Parameter	Type	Description
`method`	`String`	Always `"evm"`
`intent`	`String`	Always `"session"`
`status`	`String`	Always `"success"`
`timestamp`	`String`	RFC 3339 response time
`channelId`	`String`	Channel ID (bytes32)
`chainId`	`Integer`	EVM chain ID, e.g. `196`
`reference`	`String`	On-chain transaction hash
`deposit`	`String`	Currently known on-chain deposit (base units)

Request example#

bash

curl --location --request POST 'https://web3.okx.com/api/v6/pay/mpp/session/close' \
--header 'Content-Type: application/json' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z' \
--data '{
  "payload": {
    "action": "close",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "cumulativeAmount": "500000",
    "voucherSignature": "0x4a5b6c7d8e9fa0b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b501",
    "payeeSignature": "0x22334455667788990011aabbccddeeff00112233445566778899aabbccddeeff1c",
    "nonce": "17890324512398000000000000000000000000000000000000000000000000000002",
    "deadline": "1745500600"
  }
}'

Response example#

json

{
  "code": "0",
  "msg": "",
  "data": {
    "method": "evm",
    "intent": "session",
    "status": "success",
    "timestamp": "2026-04-01T12:04:30Z",
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "chainId": 196,
    "reference": "0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890",
    "deposit": "10000000"
  }
}

5. /api/v6/pay/mpp/session/status#

GET

/api/v6/pay/mpp/session/status

Query the current state of a payment channel (read-only).

Request parameters#

Parameter	Location	Type	Required	Description
`channelId`	query	`String`	Yes	Channel ID (bytes32 hex)

Response parameters#

Parameter	Type	Description
`channelId`	`String`	Channel ID (bytes32)
`payer`	`String`	Payer address
`payee`	`String`	Payee address
`token`	`String`	ERC-20 token contract address
`deposit`	`String`	Total deposit amount (base units)
`settledOnChain`	`String`	Amount already settled on-chain (only updated after `settle` is called)
`sessionStatus`	`String`	Channel state: `OPEN` / `CLOSING` / `CLOSED`
`remainingBalance`	`String`	Remaining balance (deposit - cumulativeAmount)

Request example#

bash

curl --location --request GET 'https://web3.okx.com/api/v6/pay/mpp/session/status?channelId=0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f' \
--header 'OK-ACCESS-KEY: 37c541a1-****-****-****-10fe7a038418' \
--header 'OK-ACCESS-SIGN: leaV********3uw=' \
--header 'OK-ACCESS-PASSPHRASE: 1****6' \
--header 'OK-ACCESS-TIMESTAMP: 2023-10-18T12:21:41.274Z'

Response example#

json

{
  "code": "0",
  "msg": "",
  "data": {
    "channelId": "0x6d0f4fdf1f2f6a1f6c1b0fbd6a7d5c2c0a8d3d7b1f6a9c1b3e2d4a5b6c7d8e9f",
    "payer": "0xaabbccddee11223344556677889900aabbccddee",
    "payee": "0x742d35Cc6634c0532925a3b844bC9e7595F8fE00",
    "token": "0xA8CE8aee21bC2A48a5EF670afCc9274C7bbbC035",
    "deposit": "10000000",
    "settledOnChain": "100000",
    "sessionStatus": "OPEN",
    "remainingBalance": "9750000"
  }
}

Common data structures#

Challenge#

The Challenge object issued by the server, echoed back by the client as-is.

Parameter	Type	Required	Description
`id`	`String`	Yes	Challenge ID
`realm`	`String`	Yes	Protection space identifier
`method`	`String`	Yes	Always `"evm"`
`intent`	`String`	Yes	Payment intent: `"charge"` / `"session"`
`request`	`String`	Yes	base64url-encoded request parameters
`expires`	`String`	Yes	Expiry time (ISO 8601)

Supported networks and tokens#

Network	Chain Index	Status
X Layer	196	Supported

Stablecoins supported on X Layer:

Token	Contract address
USDG	`0x4ae46a509f6b1d9056937ba4500cb143933d2dc8`
USD₮0	`0x779ded0c9e1022225f8e0630b35a9b54be713736`

Error codes#

Error responses use the unified envelope {"code": "<code>", "msg": "<message>", "data": null}.

1. Authentication errors (HTTP 401)#

Code	Description
50103	Header `OK-ACCESS-KEY` cannot be empty
50104	Header `OK-ACCESS-PASSPHRASE` cannot be empty
50105	Header `OK-ACCESS-PASSPHRASE` is invalid
50106	Header `OK-ACCESS-SIGN` cannot be empty
50107	Header `OK-ACCESS-TIMESTAMP` cannot be empty
50111	Invalid `OK-ACCESS-KEY`
50112	Invalid `OK-ACCESS-TIMESTAMP`
50113	Invalid signature

2. Request errors#

Code	HTTP status	Description
50011	429	User request rate exceeds the per-endpoint limit
50014	400	Required parameter `{param}` cannot be empty

3. Business errors#

Code	Name	Description
8000	SERVICE_ERROR	Internal API service error
70000	invalid_params	Missing required field or invalid format
70001	unsupported_chain	Chain is not in the supported list
70002	payer_blocked	Payer is blocklisted
70003	invalid_credential	source missing, or txHash already used
70004	invalid_signature	Signature verification failed
70005	split_sum_exceeds_total	Split total >= primary amount
70006	split_count_exceeded	Split count > 10
70007	tx_not_confirmed	Transaction not confirmed on-chain
70008	channel_close	On-chain contract channel is already closed
70009	challenge_invalid	Challenge does not exist or has expired
70010	channel_not_found	channelId does not exist
70011	grace_period_too_short	Escrow contract grace period under 10 minutes — channel open rejected
70012	amount_exceeds_deposit	cumulativeAmount exceeds the channel's deposit balance
70013	voucher_delta_too_small	Voucher increment below minVoucherDelta
70014	channel_closing	Channel is in CLOSING state and won't accept new Vouchers

Table of contents

Authentication

1. /api/v6/pay/mpp/session/open

2. /api/v6/pay/mpp/session/topUp

3. /api/v6/pay/mpp/session/settle

4. /api/v6/pay/mpp/session/close

5. /api/v6/pay/mpp/session/status

Common data structures

Error codes