42920: Connection terminated by a fatal rate limit

The connection was closed because a rate limit was exceeded severely enough to be treated as fatal, rather than rejecting individual operations. This is the general form of a fatal rate-limit close; common cases have their own codes.

What you should do

The error message names the metric for the limit involved. Reduce the rate of the operation it identifies before reconnecting, otherwise the connection will be closed again if the behavior continues.

Why it happens

Most rate limits reject individual operations without closing the connection. When a breach is severe or sustained enough, Ably closes the connection instead. This code is the general form of such a fatal close; specific cases have their own codes, such as 42921 for per-connection publishing and 42924 for protocol messages.

What you'll see

The connection is closed. The error is reported with code 42920 and HTTP status 429.