> ## Documentation Index > Fetch the complete documentation index at: https://docs.atum.xyz/llms.txt > Use this file to discover all available pages before exploring further. # Get chain defaults > Fetch the Payment Gateway's live chain defaults: contract addresses per CAIP-2 chain, and which chains you can actually pay on, instead of hardcoding them. Fetch these addresses at startup rather than hardcoding them — they change when a chain's contracts are redeployed. With no `chain_id` you get every chain the gateway serves, which also makes this the simplest check that the gateway is reachable. A chain that isn't fully configured is left out of that listing, and an empty address is a chain you cannot pay on. See [Contract addresses](/get-started/reference/contract-addresses). ## OpenAPI ````yaml GET /v1/defaults openapi: 3.0.3 info: title: Atum Payment Gateway API description: > The Atum Payment Gateway API enables secure, cross-chain payments with built-in escrow protection and settlement verification. This API facilitates decentralized payment routing across multiple blockchain networks while ensuring transaction atomicity and settlement guarantees. ## Supported Blockchains - Ethereum and EVM-compatible chains (Arbitrum, Optimism, Base, etc.) - Solana - Tron ## Authentication No API key, token, or authorization header is required on any operation. A payment carries its own authorization: the `sender_auth` signed messages prove control of the funding account, and are verified on every submission. version: 1.0.0 servers: - url: https://payment-gw.production-mainnet.atum.xyz description: Mainnet - url: https://payment-gw.production-testnet.atum.xyz description: Testnet security: [] tags: - name: Payments description: >- Submit a payment and follow it to settlement, by payment id, by your own request id, or step by step. - name: Authorizations description: Counterparty authorization requested while a payment is being accepted. - name: Quote Requests description: >- The two-phase quote flow - open a quote-request batch, poll it, then award one quote. - name: Chain Defaults description: >- The per-chain corridor addresses a client needs before it can build and sign a payment. - name: Health description: Liveness probe for the gateway. paths: /v1/defaults: get: tags: - Chain Defaults summary: Get chain defaults description: > The addresses needed to build a payment on a chain: the escrow, the accounts named in the deposit authorization, and the fulfillment verifier. Fetch these rather than hardcoding them - they change when a chain's contracts are redeployed. With `chain_id`, returns that chain. Without it, or with an empty value, returns every chain the gateway serves, keyed by CAIP-2 chain id. A chain that is not fully configured is still returned when asked for by `chain_id`, with the missing address empty, but is left out of the full listing. Treat an empty address as a chain you cannot pay on. operationId: getDefaults parameters: - name: chain_id in: query required: false description: >- CAIP-2 chain identifier. Omit it, or send it empty, to receive every chain the gateway serves, keyed by chain id. schema: type: string example: eip155:84532 responses: '200': description: >- Chain defaults. A single object when `chain_id` was supplied, otherwise an object keyed by CAIP-2 chain id. content: application/json: schema: $ref: '#/components/schemas/GetDefaultsResult' '400': description: The `chain_id` is not a valid CAIP-2 chain identifier content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '404': description: >- The requested chain is not served by this gateway, or - when `chain_id` was omitted - no chain could be resolved at all content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '503': description: A dependency is temporarily unavailable content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' components: schemas: GetDefaultsResult: description: >- Either one chain's defaults or every chain keyed by CAIP-2 chain id, depending on whether `chain_id` was supplied. A top-level `chain_id` identifies the first. oneOf: - $ref: '#/components/schemas/ChainDefaults' - $ref: '#/components/schemas/ChainDefaultsByChain' ErrorResponse: type: object description: >- Safe, outward-facing error. Derived from an internal error through the shared error catalog. The public code identifies the category and the message is a curated, safe description. A panic is caught by shared middleware that responds `{"error": "Internal server error occurred"}` instead, so a 500 is not guaranteed to carry this shape. required: - code - message properties: code: type: string description: Public, machine-readable error category in SCREAMING_SNAKE_CASE. pattern: ^[A-Z][A-Z0-9_]*$ example: INVALID_SOURCE_ASSET message: type: string description: Curated, safe, human-readable message. maxLength: 500 example: The source asset identifier is not a valid CAIP-19 asset. request_id: type: string description: >- Correlation id to quote to support to locate the internal error record. example: req_123456789 payment_id: type: string description: >- The payment this error was raised against. Absent when the error is not about a specific payment. example: '0xc7108e200d11580e7e75185991084b42a535af588ba8267cd0d1e7df089e5c9c' docs_url: type: string format: uri description: Link to the documentation page for this public code. domain: type: string description: Originating service domain. example: PAYMENT_GATEWAY retry_classification: type: string description: >- What the caller should do next. Absent means the condition has not been classified, which is not the same as safe to retry. Re-sending the same `request_id` is an idempotent replay and always safe. This value is about submitting a new one, which starts a new operation. See https://docs.atum.xyz/errors for the value set. example: RECONCILE_THEN_DECIDE request_id_reusable: type: boolean description: >- Whether the caller may re-send this same request_id. True means no payment was created for it, so the id is still free. False means a payment exists for it, so the id is spent and re-sending only replays this outcome. Absent means undetermined, which a caller should read as false. Separate from retry_classification, which answers what the caller must change rather than whether the id survived. example: false ChainDefaults: type: object description: > The addresses for one chain. Optional fields appear only where they apply to that chain; an absent optional field is not an error. required: - chain_id - quote_selector - escrow_contract - fulfillment_proxy - fulfillment_verifier properties: chain_id: type: string description: >- CAIP-2 identifier of the chain these defaults describe, normalised to lower case. example: eip155:84532 quote_selector: type: string description: >- The account named as the reserver in the deposit authorization. Sign against this exact value; a deposit reserved by anyone else is rejected. example: '0xd0f080E23F95571D26eEb1FAD24a5F3d66835195' escrow_contract: type: string description: >- The escrow the deposit is made into, and the spender of the token approval. Empty when the chain is not fully configured. example: '0xa61a0C025943Aa79B73D8D07E3aDbEe1873738b4' fulfillment_proxy: type: string description: >- The contract that pays the receiver. Read this from the DESTINATION chain's defaults, not the source chain's. Empty when the chain is not fully configured. example: '0x09A5a0d6955E5394A661Cd9E7007076fa63B4158' fulfillment_verifier: type: object description: The service that attests settlement, and the account it signs with. required: - account - endpoint properties: account: type: string description: >- The account named as the releaser in the deposit authorization. Sign against this exact value. example: '0x27050EE47befC43F4dF7807a7AA8073039e5fa89' endpoint: type: string format: uri description: Base URL of the fulfillment verifier serving this chain. example: https://veri-fill.example.com permit2_contract: type: string minLength: 1 description: >- The Permit2 this chain's escrow verifies against, sent only when it is not the canonical deployment. When absent, use the canonical Permit2 address for the chain. EVM and Tron only. example: '0x000000000022D473030F116dDEE9F6B43aC78BA3' deposit_witness_version: type: integer minimum: 3 description: >- Which deposit witness this chain's escrow expects. `4` and above select the four-member witness, `3` the two-member one; absent means four. EVM and Tron only - on Solana this is carried by `svm_signature_domain_version`. example: 4 tokens: type: array description: >- Tokens this chain's escrow accepts for deposit. Absent when the gateway has no listing for the chain, which does not mean no token is accepted. items: type: object required: - symbol - address - decimals properties: symbol: type: string example: USDC address: type: string description: Token contract address, in the chain's native address format. example: '0x036cbd53842c5426634e7929541ec2318f3dcf7e' decimals: type: integer description: Decimal places, for converting a human amount to base units. example: 6 svm_signature_cluster_id: type: string description: >- Solana only. The cluster the escrow's signing domain is bound to, needed to build the deposit hash. Absent for EVM and Tron. example: devnet svm_signature_domain_version: type: integer minimum: 1 description: >- Solana only. Version of the escrow's signing domain. Absent for EVM and Tron. example: 2 ChainDefaultsByChain: type: object description: >- Defaults for every chain the gateway serves, keyed by CAIP-2 chain id. Each key repeats the `chain_id` of the value it maps to. additionalProperties: $ref: '#/components/schemas/ChainDefaults' example: eip155:84532: chain_id: eip155:84532 quote_selector: '0xd0f080E23F95571D26eEb1FAD24a5F3d66835195' escrow_contract: '0xa61a0C025943Aa79B73D8D07E3aDbEe1873738b4' fulfillment_proxy: '0x09A5a0d6955E5394A661Cd9E7007076fa63B4158' fulfillment_verifier: account: '0x27050EE47befC43F4dF7807a7AA8073039e5fa89' endpoint: https://veri-fill.example.com ````