40031: Invalid client-specified message id

A publish was rejected because a client-supplied message id was missing, empty, or not in the required format. When several messages are published together, every message must carry a valid id following the expected pattern.

What you should do

When you assign your own message ids and publish several messages atomically, give every message an id derived from one base id, in the form <base id>:<index> (foo:0, foo:1, foo:2, and so on). If you need each message to be independently idempotent, publish them separately or use the batch publish API instead.

Why it happens

A client-specified message id acts as an idempotency key. For messages published atomically in one call, Ably requires all ids to share a single base id with a positional suffix, so the idempotency scope of the group is unambiguous. An id that is missing, empty, not a string, or that doesn't follow the <base id>:<index> pattern is rejected.

What you'll see

The error is reported with code 40031 and HTTP status 400. The messages include Client-specified message id cannot be empty and Client-specified message ids do not match the required format for multi-message ProtocolMessages.