The SMS app has an exclamation point. What does that mean?

The message was not sent successfully. If the icon of SMS app on the main screen has a red bubble and is marked with an exclamation point, it means that any message has not been sent successfully, which is the only sign of unfinished messages. If the SMS can't be sent out, first confirm whether the mobile phone is in arrears, check whether the flight mode is turned on, and turn off the flight mode.