Hey there Alepato, welcome to our Community Forum and sorry if you're having problems registering for an online mobile account with us. Can you confirm what page the error message pops up? E.g. is it on the same page as your name or is it at the end? If you've received the details and have entered everything correctly, it should let you register.
Please can you try clearing your browser cache and trying again or try a different browser so we can rule it out?