For me, I can login when I go to that first link, and then it redirects to an error page. If I try going to the link again, it says it needs to verify my and asks to send a code by text or email. I picked email, got the code, entered it--and it tells me to enter a valid code.

Were you ever T-Mobile postpaid? I was, and it appears that their prepaid and postpaid systems are partly shared, partly separate. I suspect that this leads to parts of their site getting confused.

I get this url https://my.t-mobile.com/account/profile/prepaid/privacy_noti...

which just jams.

This url from elsewhere in the thread works. or at least loads. I have no idea if it actually does anything.

https://my.t-mobile.com/account/profile/privacy_notification...

It is interesting that the one that you say works is the exact first link in my post. So it didn't work but then did work?

Sounds like they've got some screwy cookie and redirect stuff going on. For full context, I logged in to my account, and then clicked on those links (which I still had to log in again for, but maybe it made a difference?).

I was, and I am pretty sure I had to create a new account when I switched.

I did have to enable some cookies... maybe try a less secure browser?