Add Multiple Callback Subscriptions

Create multiple callback subscriptions in a single request.

This endpoint allows you to create callback subscriptions for multiple event types and callback URLs. Callback subscriptions are identified by the combination of event type and callback URL. If a callback subscription with the same event type and callback URL already exists, it will be included in the response but not created again.

Semantics:

• Multiple callback subscriptions per event type are now allowed, as long as they have different callback URLs
• Existing callback subscriptions with matching event type and callback URL are not changed, but included in the response
• Only the callback subscriptions specified in the request are affected; other existing callback subscriptions remain unchanged
• At most 42 callback subscriptions per event type are allowed