--- title: "Estimates fees for a sponsored (gasless) transaction." method: POST path: "/api/v1/relayers/{relayer_id}/transactions/sponsored/quote" tags: ["Relayers"] --- # Estimates fees for a sponsored (gasless) transaction. `POST /api/v1/relayers/{relayer_id}/transactions/sponsored/quote` This endpoint provides fee estimation for transactions where the relayer will pay the network fees on behalf of the user. The user pays fees in a token of their choice (e.g., USDC) instead of the native network currency (e.g., XLM for Stellar). The endpoint accepts either a pre-built transaction XDR or a set of operations to build a transaction from. It returns the estimated fee amount in the specified fee token and the conversion rate from the native currency. ## Path parameters - `relayer_id` string, required ## Request body - union — Network-agnostic fee estimate request parameters for gasless transactions. Contains network-specific request parameters for fee estimation. The network type is inferred from the relayer's network configuration. For Stellar, supports both classic and Soroban gas abstraction: - Classic: Pass operations or transaction_xdr with classic fee token (native/USDC:GA...) - Soroban: Pass transaction_xdr containing InvokeHostFunction, user_address, and contract fee token (C...) - SolanaFeeEstimateRequestParams - `fee_token` string, required - `transaction` string, required - StellarFeeEstimateRequestParams - `fee_token` string, required — Asset identifier for fee token. For classic: "native" or "USDC:GA5Z..." format. For Soroban: contract address (C...) format. - `operations` OperationSpec[], nullable — Operations array to build transaction from Mutually exclusive with transaction_xdr field - union - object - `amount` string, required — Amount in stroops, encoded as a decimal string to preserve precision. - `asset` union, required - object - … - object - … - object - … - `destination` string, required - `type` 'payment', required - object - `args` unknown[], required - unknown - `auth` union — Authorization specification for Soroban operations - object — No authorization required - … - object — Use the transaction source account for authorization - … - object — Use specific addresses for authorization - … - object — Advanced format - provide complete XDR auth entries as base64-encoded strings - … - `contract_address` string, required - `function_name` string, required - `type` 'invoke_contract', required - object - `auth` union — Authorization specification for Soroban operations - object — No authorization required - … - object — Use the transaction source account for authorization - … - object — Use specific addresses for authorization - … - object — Advanced format - provide complete XDR auth entries as base64-encoded strings - … - `constructor_args` unknown[], nullable - unknown - `salt` string, nullable - `source` union, required — Represents the source for contract creation - object - … - object - … - `type` 'create_contract', required - `wasm_hash` string, required - object - `auth` union — Authorization specification for Soroban operations - object — No authorization required - … - object — Use the transaction source account for authorization - … - object — Use specific addresses for authorization - … - object — Advanced format - provide complete XDR auth entries as base64-encoded strings - … - `type` 'upload_wasm', required - `wasm` union, required — Represents different ways to provide WASM code - object - … - object - … - `source_account` string, nullable — Source account address (required when operations are provided) For sponsored transactions, this should be the user's account address - `transaction_xdr` string, nullable — Pre-built transaction XDR (base64 encoded, signed or unsigned) Mutually exclusive with operations field. For Soroban gas abstraction: pass XDR containing InvokeHostFunction operation. ## Response `200` Fee estimate retrieved successfully - ApiResponseSponsoredTransactionQuoteResponse - `data` union — Network-agnostic fee estimate response for gasless transactions. Contains network-specific fee estimate results. - SolanaFeeEstimateResult - `conversion_rate` string, required - `estimated_fee` string, required - StellarFeeEstimateResult - `conversion_rate` string, required — Conversion rate from XLM to token (as string) - `fee_in_token` string, required — Estimated fee in token amount (raw units as string) - `fee_in_token_ui` string, required — Estimated fee in token amount (decimal UI representation as string) - `max_fee_in_token` string, nullable — Maximum fee in token amount (raw units as string). Only present for Soroban gas abstraction - includes slippage buffer. - `max_fee_in_token_ui` string, nullable — Maximum fee in token amount (decimal UI representation as string). Only present for Soroban gas abstraction - includes slippage buffer. - `error` string - `metadata` PluginMetadata - `logs` LogEntry[], nullable - `level` 'log' | 'info' | 'error' | 'warn' | 'debug' | 'result', required - `message` string, required - `traces` unknown[], nullable - unknown - `pagination` PaginationMeta - `current_page` integer, required - `per_page` integer, required - `total_items` integer, required - `success` boolean, required ## Other responses - `400` — Bad Request - Invalid request parameters - `401` — Unauthorized - `404` — Not Found - `429` — Too Many Requests - `500` — Internal server error ## Changes - **2026-06-05** `97fada1b2001` — 2 breaking - added the pattern `^-?[0-9]+$` to the request property `oneOf[#/components/schemas/StellarFeeEstimateRequestParams]/operations/items/oneOf[subschema #1]/amount` - the `oneOf[#/components/schemas/StellarFeeEstimateRequestParams]/operations/items/oneOf[subschema #1]/amount` request property type changed from `integer` to `string`, and format from `int64` to no format - **2026-02-09** `6408963b7c93` — 2 info - added the optional property `data/oneOf[#/components/schemas/StellarFeeEstimateResult]/max_fee_in_token` to the response with the `200` status - added the optional property `data/oneOf[#/components/schemas/StellarFeeEstimateResult]/max_fee_in_token_ui` to the response with the `200` status - **2025-12-02** `b62ae34bc27a` — 1 info - endpoint added - **2025-10-31** `5487da58bf15` — 1 breaking - api path removed without deprecation [Change history](https://skmtc.dev/openzeppelin/apis/openzeppelin-relayer-api/changes/api/v1/relayers/:relayer_id/transactions/sponsored/quote/post.md) --- [API](https://skmtc.dev/openzeppelin/apis/openzeppelin-relayer-api.md) · [All operations](https://skmtc.dev/openzeppelin/apis/openzeppelin-relayer-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/openzeppelin/openzeppelin-relayer-api/revisions/e6e7514284f5/schema)