RainLoop authentication failed while there are no log files

I just have installed CyberPanel and configuring SSL on hostname which is working fine.
I also have created an email account and when I refer to RainLoop to login, I see Authentication Failed error message while I’m sure I enter the correct password.

Would you please help me?
I also tried seeing logs at /var/log, but I see no log files like maillog or mail.log.

Please don’t tell me:
1- Check admin dashboard, because I can login there fine.
2- Check my email password because I’m sure of it.

Thanks in advance