Rules & limits

Validation failures return HTTP 422 with a body of the form { "status": 422, "error": "<message>" }. A subscription that doesn't belong to your token returns 404, and a missing or invalid token returns 401/403.

Condition	HTTP	Error message
Subscriptions per token exceed the allowed maximum	422	`"Webhook subscriptions limit reached for this subscriber"`
Same token + same callback URL already has a subscription sharing at least one event	422	`"A subscription already exists (ID …) with these events (…) and callback URL (…)"`
An event name in `events` is not recognized	422	The unknown event names are listed
Token lacks a scope granting read access to an event's resource	422	The event and its accepted scopes are listed
`callback_url` is not a valid HTTPS URL	422	`"Callback url must be a valid HTTPS URL"`
Subscription not found or belongs to another token	404	`"Webhook subscription was not found"`

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Fan-out to multiple endpoints
The same event can be delivered to different callback URLs — the overlap check only applies when the callback URL is identical. This lets you route a single event to multiple downstream services.

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Missing scopes do not block subscription creation
Subscribing to an event you don't have scope for is allowed. Pennylane simply skips deliveries for that event until your credential holds the required scope — see Scopes above.