Hi @RbDev,
I’ve tried to reproduce your issue on a v5.12.1 server on app version 1.21.0 (build 206) and I am not able to. Messages send fine for me. If I disconnect my internet connection and send a message, I get the “i” next to the message and a notification that I have no connection. When I reconnect and tap on the “i” and “try again” the message is sent successfully.
Are you able to update your device to the latest version?