### Mark an invoice unpaid

`POST /api/v1/users/{id}/invoices/{invoiceId}/unpay`

Reverses the paid stamp. Again, bookkeeping only.

- Authentication: manager session (JWT) or API token
- Permission: `prm_users_invoices_edit` (Edit / pay user invoices)
- Risk: write
- Rate limit bucket: `t_mutate`

#### Parameters

| Name | In | Type | Required | Description |
| --- | --- | --- | --- | --- |
| `id` | path | integer | yes | Subscriber id. |
| `invoiceId` | path | integer | yes | Invoice id. |