X_NOTIFY_PUSH_MESSAGE_INVALID
Means
a data-only push carries more than an id
Typical cause
the data of a data-only push names a reserved key, holds more than 8 keys, or a value longer than 256 characters
Fix
pushChannel({ pusher, data: ({ event }) => ({ id: event.params.id }) }) — in the notifier: one id per push, the app fetches the rest over its API