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

# Pay-As-You-Go Billing Override

> Force pay-as-you-go billing for subscription-included models

# Pay-As-You-Go Billing Override (API)

This override forces a request to be treated as paid (pay-as-you-go), even when the user has an active subscription and the model is subscription-included.

## What It Does

* Forces a request to be treated as paid (pay-as-you-go).
* Bypasses subscription coverage for that request.
* Allows saved provider preferences to apply to subscription-included traffic.
* Does not change which models support provider selection.

## When to Use It

Use `billing_mode: "paygo"` when:

* A subscriber wants to force pay-as-you-go billing without selecting a provider in the request.
* A subscriber wants saved provider preferences to apply to subscription-included traffic.

Explicit per-request provider selection already uses pay-as-you-go billing. If a subscriber sends `X-Provider` for a subscription-included model, the request is charged at the selected provider price and does not need `X-Billing-Mode: paygo`.

## Supported Inputs

**Header**

* `X-Billing-Mode: paygo` (header name is case-insensitive)
* `x-billing-mode` is also accepted

**Body (all endpoints)**

* `"billing_mode": "paygo"`
* Alias: `"billingMode": "paygo"`

**Accepted values (case-insensitive)**

* `paygo`
* `pay-as-you-go`
* `pay_as_you_go`
* `paid`
* `payg`

**Precedence**: Body value wins if both body and header are present.

## API Examples

Example with explicit provider selection:

```http theme={null}
POST /api/v1/chat/completions
X-Provider: deepinfra
Content-Type: application/json

{
  "model": "openai/gpt-oss-20b",
  "messages": [
    { "role": "user", "content": "Say hello in one sentence." }
  ]
}
```

Example forcing paygo without explicit provider selection:

```http theme={null}
POST /api/v1/chat/completions
X-Billing-Mode: paygo
Content-Type: application/json

{
  "model": "openai/gpt-oss-20b",
  "messages": [
    { "role": "user", "content": "Say hello in one sentence." }
  ]
}
```

Responses:

```http theme={null}
POST /api/v1/responses
X-Billing-Mode: paygo

{
  "model": "gpt-4o-mini",
  "input": "Hello"
}
```

## Provider Selection Notes

* Provider selection only works for models that support it.
* If a model does not support provider selection, `X-Provider` is ignored.
* `X-Provider` explicitly selects a provider for the request.
* Explicit provider selection is always pay-as-you-go and is charged at the selected provider's price, including provider-selection markup.
* For subscription users, sending `X-Provider` bypasses subscription coverage for that request. You do not need to also send `X-Billing-Mode: paygo`.
* You cannot currently force a provider and have that same request count as subscription-included usage.

## Subscription and Limits Behavior

When `billing_mode: "paygo"` is set:

* The request is not eligible for subscription coverage.
* Subscription quota is not consumed.
* Pay-as-you-go balance checks apply as normal.

If `subscription.enablePaidModelsApi` is `false`, the request is rejected (same as any other paid API request).

## FAQ

**Does this affect which models are available?**
No. It only changes billing eligibility. Model availability is unchanged.

**Does it force a provider for non-selectable models?**
No. It only affects billing. Use `X-Provider` to explicitly select a provider for models that support provider selection.

**Can I combine this with BYOK?**
Yes. BYOK still works; paygo override only changes subscription eligibility.