Upon further investigation, it is not possible to activate logs for the Quectel LTE EC25 modem.
Therefore, I think you can also be guided by the response of the AT commands after their execution. For example, after sending the message through the "AT+CMGS=" command, you receive a "+CMGS=" confirmation, and then an "OK". You can use some method to read the serial port and verify these responses after sending your message. Reading what the AT commands return will help you to debug your app, that because each response is different depending on the type of command and error.