Any Help PLEASE for F451 Error

@RayDawnk I don't use a user name when I log into the T-Mobile website, I use my T-Mobile gateway assigned phone number. I guess you can create a username for your account once you log in to the website. so, is you use your phone number and password you created in the beginning you should be able to log into the T-Mobile website. 

I have not seen that error message before. It looks like other people have experience the issue as well: 

Here is another thread on the topic, but a solution is included: 

Best answer by batrimmer

I had this problem when I first signed up for home internet.  It had to do with my having a very old (and long inactive) prepaid hotspot linked to my e-mail address.  I had to call Home Internet Customer Service, and they basically had to remove the e-mail address from my account.  The person on the phone couldn't do this - they had to escalate it to someone else and call back the next day.  When they called me back, they had to manually add my e-mail (as though I had never given them an e-mail when I signed up).  After that, it worked fine.

Just make sure you call Home Internet Customer Service at 1-844-275-9310  instead of the regular customer service number.

I hope this helps!