The store. Where you use mine coins . Look also my problem for more info https://bugs.mojang.com/browse/MCPE-40773
I have the same problem on iPad 2018. I cannot connect neither in the Xbox live nor in the marketplace . Also the same problem occurs in the Xbox live app . I cannot connect there . My account is okay and the internet connection too.
The problem is now solved. I just opened Minecraft and got connected. Thank you