Managing presence indicators such as Available, Busy, or Away in Teams Free
After spending some time with a person on the support chat I found a solution that worked for me. The reason why I could not add a billing address was because my language was not set. You do have to set a country / region and language in your account info. After that I was able to add a billing address. I also did all these things in an Incognito Chrome browser, but I do believe this was unnecessary and would have likely also worked in any other browser / non-incognito. Hope this helps someone!