Hello Ines
this is typical if you messed up with redirections at your registrar
the part that is probably wrong is the 301 redirect, you need to redirect the root domain (without www) to http://www.yourdomain.com
you maybe did the opposit (redirecting www to root domain)
Another common error is if you kept an A record for WWW
you need to delete it and create a CNAME for WWW pointing to custom-domain.appdrag.com