Unable to purchase Roblox premium or robux using my microsoft balance

Question

I think the title's self explanatory, recently, I've gotten a 5$ USD microsoft giftcard from their program and it was added to my microsoft balance, but while trying to purchase Robux, my microsoft balance doesn't come up as a payment method and while trying to buy premium, it's just a white blank space so I can't do it at all.

Someone told me to buy it from here: https://www.microsoft.com/en-us/store/search/games?q=robux&devicetype=xbox&rtc=1 But whenever I try to do that, microsoft logs me out for some reason, my balance will expire soon so I need help asap.