42911: Per-connection publish rate exceeded

A message was rejected because the connection published messages faster than the per-connection publish rate limit allows. Publishing far above the limit can escalate to the connection being closed.

What you should do

If the message matters, republish it after a short delay, increasing the delay if it is rejected again.

To stay within the limit, consider spreading publishing across more connections, since the limit applies to each connection on its own. If a single connection genuinely needs a higher rate, you can request a higher limit.

Why it happens

Each connection has a maximum rate at which it can publish messages, set by your account's limits. The limit covers everything this connection publishes across all the channels it is attached to, so it is reached when a single connection publishes too quickly overall, regardless of what other connections are doing.

What you'll see

The publish is rejected and the message is not delivered. The connection stays open. The error is reported with code 42911 and HTTP status 429, with a message of the form Rate limit exceeded; request rejected (nonfatal); metric = connection.inboundRate; ....