> ## Documentation Index > Fetch the complete documentation index at: https://docs.buckspay.xyz/llms.txt > Use this file to discover all available pages before exploring further. # Get an EVM swap quote > Get a gasless EVM token swap quote. Requires the relayer to be configured with a `swapChain` (see `FacilitatorOptions`). Returns a quote ID, expected amounts, and EIP-712 typed data for the swap authorization. **This endpoint is available only when the EVM swap rail is configured.** If `swapChain` is absent, `BuckspayClient.swap()` fails with `SWAP_FAILED`. ## OpenAPI ````yaml /api-reference/openapi.json post /swap/quote openapi: 3.1.0 info: title: Buckspay Facilitator & BFF API version: 0.2.0 description: >- HTTP wire contract for the Buckspay SDK. The SDK calls these endpoints internally via `@buckspay/relayer`; this reference is for teams building their own BFF relay route or calling the facilitator from server-side code. All facilitator endpoints require the `x-api-key` header. **The API key is a server-side secret - it must only appear in BFF or server-side code and must never be shipped to a browser bundle.** Use `createRelayRoute` and `createSignerProxyRoute` from `@buckspay/nextjs` to build compliant BFF handlers. servers: - url: '{facilitatorUrl}' description: >- Buckspay facilitator (all endpoints). Set via BUCKSPAY_FACILITATOR_URL on the server. variables: facilitatorUrl: default: https://facilitator.buckspay.xyz description: Base URL of the Buckspay facilitator service. security: - FacilitatorApiKey: [] tags: - name: Relay description: >- Submit a signed Soroban authorization entry for gasless relaying to the Stellar network. - name: Fee description: >- Quote the fee-token amount required for gas-in-token (token gas mode) before building the forward() invocation. - name: Account State description: Read on-chain state for classic G-addresses and contract C-addresses. - name: Onboarding description: >- Build and submit the sponsored onboarding transaction; deploy passkey smart-accounts and policy session-accounts. - name: Auth description: >- Signer-proxy for social and email authentication. The BFF forwards these requests to the facilitator; provider secrets remain server-side. - name: Swap description: >- Quote a gasless EVM token swap. Requires `swapChain` to be configured in the relayer. paths: /swap/quote: post: tags: - Swap summary: Get an EVM swap quote description: >- Get a gasless EVM token swap quote. Requires the relayer to be configured with a `swapChain` (see `FacilitatorOptions`). Returns a quote ID, expected amounts, and EIP-712 typed data for the swap authorization. **This endpoint is available only when the EVM swap rail is configured.** If `swapChain` is absent, `BuckspayClient.swap()` fails with `SWAP_FAILED`. operationId: postSwapQuote requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/SwapQuoteRequest' responses: '200': description: Swap quote computed. content: application/json: schema: $ref: '#/components/schemas/SwapQuoteResponse' '400': description: Swap quote failed (pair not supported, slippage too high, etc.). content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: SWAP_FAILED message: pair not supported on this chain '401': description: Invalid or missing API key. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' components: schemas: SwapQuoteRequest: type: object required: - chain - payer - merchant - sellToken - buyToken - sellAmount properties: chain: type: string enum: - avalanche - celo - polygon - base - avalanche-fuji - polygon-amoy - base-sepolia - celo-sepolia description: >- EVM chain for the swap. Must match the `swapChain` configured in `buckspayFacilitator`. payer: type: string description: EVM address of the payer (0x-prefixed). merchant: type: string description: >- EVM address where the buy-token is settled. For self-custody swaps this equals `payer`. sellToken: type: string description: EVM contract address of the sell token. buyToken: type: string description: EVM contract address of the buy token. sellAmount: allOf: - $ref: '#/components/schemas/Stroops' description: >- Amount to sell in the sell token's minimal units, as a decimal string. description: >- Request body for `POST /swap/quote`. Corresponds to the body built in `buckspayFacilitator.quoteSwap()`. SwapQuoteResponse: type: object required: - quoteId - sellAmount - expectedBuyAmount - minBuyAmount - typedData - needsAuthorization - source - expiresAt properties: quoteId: type: string format: uuid description: Unique identifier for this quote. sellAmount: allOf: - $ref: '#/components/schemas/Stroops' description: Actual sell amount (may differ from requested amount after routing). expectedBuyAmount: allOf: - $ref: '#/components/schemas/Stroops' description: Expected amount of buy token received. minBuyAmount: allOf: - $ref: '#/components/schemas/Stroops' description: >- Minimum buy amount after slippage. The client enforces this floor before submitting. typedData: type: string description: >- EIP-712 typed data string for the swap authorization. Required if `needsAuthorization` is `true`. needsAuthorization: type: boolean description: >- Whether the payer must sign the EIP-712 `typedData` before submitting the swap. source: type: string description: Liquidity source or aggregator used to build the quote. expiresAt: type: string description: ISO 8601 timestamp after which the quote is invalid. description: >- Swap quote returned by `POST /swap/quote`. Mirrors the `swapQuoteResponseSchema` zod schema in `@buckspay/relayer`. ErrorResponse: type: object required: - error properties: error: type: string description: >- Machine-readable error code. SDK error codes (e.g. `RELAYER_REJECTED`, `SESSION_POLICY_VIOLATION`) or raw facilitator codes (e.g. `auth_expired`, `simulation_failed`) depending on context. message: type: string description: >- Optional human-readable detail. Never log raw upstream messages - they may contain addresses or sensitive information. details: type: object description: >- Optional structured validation errors (present on BFF-level schema failures). description: >- Error body returned on non-2xx responses. The `error` field maps to a `BuckspayErrorCode` or a raw facilitator error string (see `mapFacilitatorError` in `@buckspay/relayer`). Stroops: type: string pattern: ^\d+$ description: >- A non-negative integer encoded as a decimal string to preserve precision. For Stellar token amounts this is the smallest unit with the asset's implied decimals (USDC = 7, i.e. stroops); the same string encoding also carries fees, nonces, and EVM swap amounts (which use their own token's decimals). securitySchemes: FacilitatorApiKey: type: apiKey in: header name: x-api-key description: >- Server-held API key. Injected by the BFF (`createRelayRoute` / `createSignerProxyRoute` from `@buckspay/nextjs`). This key must only appear in server-side code and must never be shipped to a browser bundle. ````