I don't know if this will ever get resolved. Please note:
Hello @MatthewHuntley,
Thank you for reaching out to the Quicken Community.
Currently, my internal systems are showing the T-Mobile biller as degraded, this means that there is an issue communicating with the servers. We are aware and working towards a fix, however, there is no current ETA.
I do apologize for any inconvenience in the meantime.