> For the complete documentation index, see [llms.txt](https://bountyv.gitbook.io/vdocs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bountyv.gitbook.io/vdocs/account/topup.md).

# Top up balance

Create a crypto payment invoice that credits your account balance once the payment confirms on-chain.

```
POST /api/v1/topup
```

Synchronous — the call itself returns immediately with an invoice link. Crediting the balance happens later, asynchronously, when the payment provider confirms the on-chain transaction (typically 1–15 minutes).

## Authentication

Requires a Bearer API key. See [Authentication](/vdocs/authentication.md).

## Request

**Content-Type:** `application/json`

| Field          | Type   | Required | Default       | Description                                                                                     |
| -------------- | ------ | -------- | ------------- | ----------------------------------------------------------------------------------------------- |
| `amount_usd`   | number | ✅        | —             | USD amount to credit. Minimum `25`, maximum `10000`                                             |
| `crypto_asset` | string | —        | `"usdttrc20"` | Which coin to pay with. Supported: `usdttrc20`, `usdterc20`, `btc`, `eth`, `ltc`, `sol`, `doge` |

`usdttrc20` (Tether on Tron) has the fastest confirmation and the lowest network fees — use it unless you specifically need another asset.

## Response

```json
{
  "topup_id": "abc123",
  "invoice_url": "https://substance-api.com/api/v1/pay/abc123",
  "amount_usd": 100,
  "status": "pending",
  "message": "Visit invoice_url to complete payment. Balance credited automatically on confirmation."
}
```

| Field         | Type   | Description                                                                       |
| ------------- | ------ | --------------------------------------------------------------------------------- |
| `topup_id`    | string | Reference ID for this top-up                                                      |
| `invoice_url` | string | URL on our domain to open in a browser to pay — proxies the upstream payment page |
| `amount_usd`  | number | The amount you requested                                                          |
| `status`      | string | Always `"pending"` on creation                                                    |
| `message`     | string | Human-readable instructions                                                       |

HTTP status: `200 OK`.

## Completing payment

`invoice_url` points at `GET /api/v1/pay/{topup_id}` — a public link with no Bearer auth required (the `topup_id` itself is the unguessable token, so it's safe to open directly in a browser or hand off to whoever is actually paying).

```
GET /api/v1/pay/{topup_id}
```

* Open it in a browser — it `302`s to the upstream payment page (card/crypto address and exact amount).
* Pay from your wallet and wait for on-chain confirmation.
* Once confirmed, your balance is credited automatically server-side — no polling or notification call is required from you.
* Confirm the credit landed by calling [`GET /api/v1/credits`](/vdocs/account/credits.md).

Requesting the pay link again after the payment has already completed, or after it has failed/expired, returns `410 Gone` instead of redirecting.

## Example

```bash
curl -X POST https://substance-api.com/api/v1/topup \
  -H "Authorization: Bearer sk_live_..." \
  -H "Content-Type: application/json" \
  -d '{"amount_usd": 100, "crypto_asset": "usdttrc20"}'
```

## Errors

| Status | When                                                                                 |
| ------ | ------------------------------------------------------------------------------------ |
| `400`  | `amount_usd` outside 25–10,000, or the request body fails validation — see `details` |
| `401`  | Missing, malformed, or revoked API key                                               |
| `403`  | Account disabled — contact support                                                   |
| `429`  | Rate limit exceeded for your key                                                     |
| `502`  | Invoice creation failed at the payment provider — safe to retry                      |
| `503`  | Top-up temporarily unavailable (payment provider not configured)                     |

The `GET /api/v1/pay/{topup_id}` redirect additionally returns `404` if the ID doesn't exist, and `410` once the payment has already been completed, has failed, or has expired.

See [Errors](/vdocs/errors.md) for the full error format.

## Pricing

Billed per call — see [Credits & pricing](/vdocs/account/credits.md) for current rates. Note that `topup` itself isn't a billable action; it's how you add funds, not spend them.


---

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