billing
POST /v1/subscriptions/{subscriptionId}/billing-rail
Choose which clock charges this subscription.
Authentication
Send an API key as a bearer token. The key must carry the billing.payment.manage permission; a key without it is refused with 403, not 404.
This endpoint takes no organisation id. Your key already identifies the organisation it belongs to, and the response is scoped to it.
Try it
Replace anything in angle brackets with your own values, and the key placeholder with a key from your dashboard.
curl -X POST https://api.zinndigital.com/v1/subscriptions/{subscriptionId}/billing-rail \
-H "Authorization: Bearer zdk_live_…" \
-H "Content-Type: application/json" \
-d '{ "rail": <string<engine, paypal>> }'Signed in? The API console in your dashboard fills in your real organisation id and your own key, and runs the request against the live API so you can see the actual response. Open this endpoint in the API console
Details
Move a subscription between the **engine** rail (we invoice and charge on the renewal date) and the **PayPal** rail (PayPal charges on its own schedule under an agreement the customer approved). ADR 0029 records the boundary: PayPal owns only *when* the money is taken — the engine still owns what is owed, tax, entitlements, dunning and suspension. ⛔⛔ **Switching to PayPal returns an `approval_url` and grants nothing.** Until the buyer approves in PayPal's own interface and PayPal sends us a **signed** `BILLING.SUBSCRIPTION.ACTIVATED` webhook, the agreement cannot charge and the subscription's clock has not started. `active` is `false` for exactly that reason. The browser's return from the approval URL is an attacker-supplied claim and is never treated as approval. Switching **away** cancels the agreement at PayPal first and unbinds second. The reverse order would hand the subscription back to the engine's renewal sweep while PayPal was still entitled to charge it — a double charge for the window between the two calls. Requires `billing.payment.manage`. `422` carries a `code`: `ALREADY_ON_RAIL`, `NO_CATALOGUE_PRICE`, `PRICE_WOULD_CHANGE` (the subscription is on a price that differs from the published one, so switching would change what the customer pays — refused rather than done quietly), `NOT_SWITCHABLE`, or `PAYPAL_REFUSED`.
Parameters
| Name | Type | Required | What it is |
|---|---|---|---|
subscriptionId (path) | Uuid | Yes | The subscription whose recurring rail is being changed. |
Request body
| Name | Type | Required | What it is |
|---|---|---|---|
rail | string<engine, paypal> | Yes | — |
Response
| Name | Type | Required | What it is |
|---|---|---|---|
rail | string<engine, paypal> | Yes | — |
approval_url | object | No | Where the buyer must approve the PayPal agreement. ⛔⛔ **Until they approve there and PayPal sends us a signed `BILLING.SUBSCRIPTION.ACTIVATED`, nothing is agreed and nothing wil… |
active | boolean | Yes | Whether the named rail is charging yet. `false` immediately after switching to PayPal — a client that rendered "you are now billed by PayPal" here would be telling the customer… |
paypal_subscription_id | string | No | — |
Errors this endpoint can return
401 · 403 · 404 · 422 · 429