Unable to add new line to my Magenta MAX Military account.

Hola,

I am unable to add a new line to my Magenta MAX Military account.

I am able to choose to bring my own device and choose to add a new SIM card, but when I get to the part about choosing to add it to my T-Mobile account, it will not let me progress any further.

I have tried different browsers, on mobile and PC as well as rebooting my browser. I've even tried different times of day, just incase T-Mobile was experiencing network congestion. Nothing has worked. This has been going on for two days.

Edit: I just tried clearing my browser cache, that did not work either.
 

Just adding a bit more information. I tried adding it through the account page. I just tried going through the drop down tab for the shop, that did not work either.