signal-cli-rest-api/doc/TROUBLESHOOTING.md

The signal-cli-rest-api docker container won't start (signal_messenger_signal-cli-rest-api_1 exited with code 0)

If your docker container stops with signal_messenger_signal-cli-rest-api_1 exited with code 0, make sure that the host port isn't already occupied by another process (see here).

Sending a message suceeds, but no message is sent

According to this signal-cli ticket here, the receive endpoint needs to be called regularily. So, if sending a message seems to work, but no message is sent, please try to call the Receive API endpoint.

Cannot send message to group - please first update your profile

If you get this message, it means that you first need to update your profile to set a name (and optionally an avatar).