> ## Documentation Index > Fetch the complete documentation index at: https://docs.passage.coinlist.co/llms.txt > Use this file to discover all available pages before exploring further. # Encode an Ondo swap for broadcast > Encodes the buy the user just confirmed and returns calldata their wallet can sign and broadcast, plus the amounts it commits to. This is the commit step: it consumes an attestation and the calldata expires, so call it once per confirmation and never poll it. Approve the swap contract for the full amount first; an allowance short of it is rejected here rather than reverting on-chain. The addresses are resolved from the offer, so the request names the asset, not the tokens. ## OpenAPI ````yaml /api-reference/openapi.json post /v1/ondo/swap/transaction openapi: 3.0.0 info: title: Frontline API version: 0.1.0 servers: - url: https://api.coinlist.co variables: {} security: [] tags: - name: DocumentSubmissions - name: KYC - name: OAuth - name: Offers - name: Ondo - name: Participations - name: Pii - name: Requirements - name: Swap - name: Token - name: Wallet - name: Wallet Ownership paths: /v1/ondo/swap/transaction: post: tags: - Ondo summary: Encode an Ondo swap for broadcast description: >- Encodes the buy the user just confirmed and returns calldata their wallet can sign and broadcast, plus the amounts it commits to. This is the commit step: it consumes an attestation and the calldata expires, so call it once per confirmation and never poll it. Approve the swap contract for the full amount first; an allowance short of it is rejected here rather than reverting on-chain. The addresses are resolved from the offer, so the request names the asset, not the tokens. operationId: createOndoSwapTransaction parameters: [] requestBody: content: application/json: schema: $ref: '#/components/schemas/OndoSwapTransactionRequest' application/x-www-form-urlencoded: schema: $ref: '#/components/schemas/OndoSwapTransactionRequest' description: Ondo swap transaction params required: true responses: '200': content: application/json: schema: $ref: '#/components/schemas/OndoSwapTransaction' description: Successful response. default: content: application/json: schema: $ref: '#/components/schemas/Error' description: Error response. callbacks: {} security: - OAuth2: [] components: schemas: OndoSwapTransactionRequest: additionalProperties: false description: 'The buy to encode: an asset, the wallet buying it, and what it pays.' properties: amount: description: >- Gross amount to pay, as a uint256 decimal string in the funding token's smallest unit. This is the figure to approve: the CoinList fee comes off it, and Ondo prices the remainder. example: '100000000' type: string chain: description: >- The EVM chain to swap on. Only chains CoinList has deployed a swap contract on are accepted, which is narrower than both this enum and the chains the on-chain reads serve. enum: - ethereum_sepolia - base_sepolia - ethereum_mainnet - base_mainnet example: ethereum_sepolia type: string symbol: description: Ondo asset symbol to buy example: AAPLon type: string wallet_address: description: >- Wallet that will broadcast the transaction. The calldata is signed over it, so no other wallet can send it. example: '0x2c4c7082a135f6b980cdae4b40c3ebf72cd4a512' type: string required: - symbol - chain - wallet_address - amount title: OndoSwapTransactionRequest type: object OndoSwapTransaction: additionalProperties: false description: >- A signed, ready-to-broadcast Ondo swap and the amounts it commits to. Unlike the quote, this spends an attestation and expires, so call it once the user has confirmed and never on a timer. properties: action: enum: - broadcast_transaction type: string data: description: The encoded swap to broadcast on-chain example: '0x0c89df8c' type: string expires_at: description: >- When the signed calldata stops being accepted. Broadcast before this or request a new transaction; a late send reverts. example: '2025-01-01T00:00:00.000000Z' format: date-time nullable: false type: string fee: description: >- CoinList's cut of pay_input_amount, in the same units. Taken at execution, not on top, so the wallet never approves more than pay_input_amount. example: '0' type: string notional_value: description: >- The part of pay_input_amount that reaches Ondo, in the same units. This is what the quantity was priced against, and the signature commits to it. example: '100000000' type: string pay_input_amount: description: >- Total the purchase costs, fee included, as a uint256 decimal string in the funding token's smallest unit. The approval has to cover this. example: '100000000' type: string pay_input_decimals: description: >- Decimals pay_input_amount, fee and notional_value are denominated in, read on-chain from the funding token. The token is resolved from the offer rather than named by the caller, so this is the only place its scale is published. example: 6 type: integer receive_output_amount: description: >- Quantity of the asset the wallet receives, as a uint256 decimal string in the asset's smallest unit. Divide by 10^receive_output_decimals to display whole tokens. example: '264000000000000000' type: string receive_output_decimals: description: >- Decimals receive_output_amount is denominated in, reported by whatever priced the quantity rather than looked up separately. example: 18 type: integer to: description: The swap contract to submit the transaction to example: '0xff9c5ade32d9b4102469bd5f3817cb0061b25fec' type: string required: - action - to - data - expires_at - pay_input_amount - pay_input_decimals - fee - notional_value - receive_output_amount - receive_output_decimals title: OndoSwapTransaction type: object Error: additionalProperties: false properties: code: description: A human-readable message providing more details about the error. type: string errors: additionalProperties: items: type: string type: array type: object event_id: description: >- The unique identifier for the error event. This is useful for tracking and debugging. type: string message: description: >- For some errors that could be handled programmatically, a short string indicating the error code reported. type: string type: description: >- The type of error returned. One of `api_error`, `invalid_request_error` enum: - api_error - invalid_request_error type: string required: - type - message title: Error type: object securitySchemes: OAuth2: description: OAuth 2.0 authorization and token endpoints flows: authorizationCode: authorizationUrl: /oauth/authorize refreshUrl: /oauth/token scopes: {} tokenUrl: /oauth/token clientCredentials: refreshUrl: /oauth/token scopes: {} tokenUrl: /oauth/token type: oauth2 ````