> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bleepay.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Submit Interop Signature

> Initiate cross-chain signature submission for a voucher.

`POST /api/v1/vouchers/:voucherId/submit/interop-init`

Initiates a cross-chain signature submission flow. Used when the voucher requires signatures across multiple blockchain networks.

## Parameters

### Path

| Name        | Type     | Required | Description    |
| ----------- | -------- | -------- | -------------- |
| `voucherId` | `string` | Yes      | The voucher ID |

### Query

| Name           | Type      | Required | Description                              |
| -------------- | --------- | -------- | ---------------------------------------- |
| `id`           | `string`  | Yes      | Signature submission identifier          |
| `paymentIndex` | `integer` | No       | Index of the payment being signed (0–10) |
| `vid`          | `string`  | No       | Voucher ID override for the signature    |

### Body

| Name        | Type     | Required | Description                                   |
| ----------- | -------- | -------- | --------------------------------------------- |
| `signature` | `string` | No       | The cryptographic signature, 1–256 characters |

## Request example

```shell theme={null}
curl --request POST 'https://payments.bleepay.com/api/v1/vouchers/vch_482916/submit/interop-init?id=sig_abc&paymentIndex=0' \
  --header 'Authorization: Bearer <payer_token>' \
  --header 'Content-Type: application/json' \
  --data '{ "signature": "0xSignature..." }'
```

## Response

Returns `{ "id": "<submission_id>" }` on success.

### Error responses

| Status | Code           | Description                     |
| ------ | -------------- | ------------------------------- |
| `401`  | `unauthorized` | Missing or invalid bearer token |
| `404`  | `not_found`    | Voucher not found               |