On a computer or phone, open the link https://account.microsoft.com/billing/payments?lang=ru-RU in Google Chrome.
I go to the account Microsoft and look at the balance (how much money is there now):

On a computer or phone, open the link https://account.microsoft.com/billing/orders?lang=ru-RU in Google Chrome.
I log in to the Microsoft account and look at the purchases:

Let's look at the country in the Microsoft account, open https://account.microsoft.com/profile?lang=en-US
Country: Germany
Payment for the countries Belarus and Russia does not work.
You can select any country from Europe or America or Turkey. I chose Germany.

Note! Buying gold coins for the countries Belarus and Russia does not work.
I open it on my phone VPN
I use this vpn and launch the country of Germany:

 
On the phone, I open Minecraft official website https://minecraft.net ...

I go to the child's profile:

 
I buy gold coins like this:

 
Everything is fine. Gold coins appeared: