> ## Documentation Index > Fetch the complete documentation index at: https://second.tech/docs/llms.txt > Use this file to discover all available pages before exploring further. # Build a BIP 321 payment URI > Builds a single BIP 321 `bitcoin:` URI bundling multiple ways to receive the same payment, so one call prepares everything needed for an incoming payment. A fresh Ark address is always included. When `amount_sat` is given, a BOLT11 invoice for that amount is generated and the amount is embedded in the URI. When `onchain` is `true`, a fresh on-chain address is added (placed in the URI body on mainnet, as a `tb=` parameter on test networks). Set the `uppercase` query parameter to upper-case the `bip321` URI so QR encoders can use the compact alphanumeric mode; this fails if the URI carries case-sensitive data. The individual `ark`, `bolt11`, and `onchain` destinations are always returned in their natural case for direct use. ## OpenAPI ````yaml https://gitlab.com/ark-bitcoin/bark/-/raw/master/bark-rest/openapi.json post /api/v1/wallet/bip321 openapi: 3.1.0 info: title: barkd REST API description: >- A simple REST API for barkd, a wallet daemon for integrating bitcoin payments into your app over HTTP. Supports self-custodial Lightning, Ark, and on-chain out of the box. barkd is a long-running daemon best suited for always-on or high-connectivity environments like nodes, servers, desktops, and point-of-sale terminals. All endpoints return JSON. Amounts are denominated in satoshis. contact: name: Second Team email: hello@second.tech license: name: MIT identifier: MIT version: 0.4.0 servers: [] security: - bearer: [] tags: - name: boards description: Move on-chain bitcoin onto the Ark protocol. - name: exits description: Move bitcoin back on-chain without server cooperation. - name: fees description: Estimate fees for wallet operations before executing them. - name: history description: Inspect and annotate wallet movement history. - name: lightning description: Create Lightning invoices and track receives. - name: onchain description: Manage barkd's on-chain bitcoin wallet. - name: wallet description: Manage Ark balances and VTXOs, send payments via Ark, LN, and on-chain. - name: bitcoin description: Query bitcoin network data. - name: notifications description: Receive real-time notifications from barkd. paths: /api/v1/wallet/bip321: post: tags: - wallet summary: Build a BIP 321 payment URI description: >- Builds a single BIP 321 `bitcoin:` URI bundling multiple ways to receive the same payment, so one call prepares everything needed for an incoming payment. A fresh Ark address is always included. When `amount_sat` is given, a BOLT11 invoice for that amount is generated and the amount is embedded in the URI. When `onchain` is `true`, a fresh on-chain address is added (placed in the URI body on mainnet, as a `tb=` parameter on test networks). Set the `uppercase` query parameter to upper-case the `bip321` URI so QR encoders can use the compact alphanumeric mode; this fails if the URI carries case-sensitive data. The individual `ark`, `bolt11`, and `onchain` destinations are always returned in their natural case for direct use. operationId: bip321_uri parameters: - name: uppercase in: query description: >- Upper-case the returned `bip321` URI for compact QR encoding. Defaults to false. Fails with 400 if the URI carries case-sensitive data (a label, message, or base58 address). required: false schema: type: boolean requestBody: content: application/json: schema: $ref: '#/components/schemas/Bip321UriRequest' required: true responses: '200': description: Returns the BIP 321 URI and its destinations content: application/json: schema: $ref: '#/components/schemas/Bip321UriResponse' '400': description: Requested an upper-case URI that carries case-sensitive data content: application/json: schema: $ref: '#/components/schemas/BadRequestError' '500': description: Internal server error content: application/json: schema: $ref: '#/components/schemas/InternalServerError' components: schemas: Bip321UriRequest: type: object description: >- Request to build a BIP 321 unified payment URI. An Ark address is always included. A BOLT11 invoice is only included when `amount_sat` is given (an amount is required to create one). An on-chain address is included only when `onchain` is `true`. properties: amount_sat: type: - integer - 'null' format: int64 description: >- Optional amount (in satoshis) to request. When set, it is embedded in the URI and used to create the BOLT11 invoice. Any server-configured [LightningReceiveFees](crate::cli::fees::LightningReceiveFees) are deducted from the amount the client ultimately receives over Lightning. minimum: 0 label: type: - string - 'null' description: >- Optional label describing the payment, recorded in the URI's `label`. message: type: - string - 'null' description: >- Optional message describing the payment, recorded in the URI's `message`. onchain: type: - boolean - 'null' description: >- Whether to include a fresh on-chain address as a payment destination. Defaults to `false`. Bip321UriResponse: type: object description: >- A BIP 321 unified payment URI together with its individual destinations. The `bip321` field is the combined `bitcoin:` URI; the other fields expose each generated destination separately for convenience. A field is `null` when that destination was not requested or could not be produced. required: - bip321 properties: ark: type: - string - 'null' description: The generated Ark address, if any. bip321: type: string description: The combined BIP 321 `bitcoin:` URI. bolt11: type: - string - 'null' description: >- The generated BOLT11 invoice, included only when an amount was given. onchain: type: - string - 'null' description: >- The generated on-chain address, included only when `onchain` was set. BadRequestError: type: object required: - message properties: message: type: string InternalServerError: type: object required: - message properties: message: type: string securitySchemes: bearer: type: http scheme: bearer bearerFormat: AuthToken description: Base64url-encoded auth token ````