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

# Calling Add-on Slots

> How many calling add-ons your workspace pays for, how many lines use them, and how many are free for the next phone line at no new charge.

> [!NOTE]
>
> Read-only. Use a **workspace** API key (`tuco_…`).

Each calling add-on your workspace pays for is a **slot**. Add-ons ticked at checkout buy one slot
for every phone line in your plan. Each phone line ordered after that takes one free slot of each
add-on automatically, with no new charge. This endpoint shows what's left.

```bash theme={null}
curl https://app.tuco.ai/api/lines/calling-addon-slots \
  -H "Authorization: Bearer tuco_xxxxxxxxxxxxx"
```

```json theme={null}
{
  "slots": {
    "facetime_audio": { "paid": 2, "held": 1, "free": 1 },
    "caller_id_registration": { "paid": 0, "held": 0, "free": 0 }
  }
}
```

One entry per add-on key (`facetime_audio`, `caller_id_registration`):

**paid** `number`

Slots of this add-on on the workspace's subscription.

**held** `number`

Lines that have this add-on (awaiting payment, setting up, or active).

**free** `number`

`paid` minus `held`, never below 0. More than 0 means the next phone line gets this add-on
automatically with no new charge, and adding it to an existing line with
[`POST /api/lines/{id}/calling-addons`](https://docs.tuco.ai/api-reference/endpoint/calling-addons) costs nothing.

A workspace without a subscription (for example, an agency workspace billed by invoice) returns
`0` for everything.

The same number is on each add-on in
[`GET /api/lines/{id}/calling-addons`](https://docs.tuco.ai/api-reference/endpoint/calling-addons) as `prepaidFree`.

## Error responses

| Status | When |
| - | - |
| `401` | Missing or invalid key |
| `403` | An agency key (`tucoagency_…`) was used |
| `502` | `"Could not read add-on slots."` Billing couldn't be read. Try again |


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