Unable to purchase Minecoins

I am trying to purchase Minecoins via the in-game Marketplace to no avail. I have tried the various paths to the purchase screen such as settings > get more packs, clicking on a texture pack > add minecoins and simply the + icon in the top right corner.

When I click on the bundle of choice, a dialogue box appears saying I am not connected to the internet (I am, and have run troubleshooting as well), or the below blank box appears and nothing happens.

I have tried adding coins via the microsoft store, via the minecraft store (where I purchased a giftcard I thought I could redeem only to find I did not scroll far enough to read the 'cannot be used to redeem minecoins' caveat, so I now have a useless store giftcard) and have found no solutions online. 

I have closed and reopened my game. I have restarted my PC. My husband somehow added money to my microsoft account though I can't work out how to transfer that into minecoins.

This is extremely frustrating. I have never had this issue before. I am finding the lack of alternative means to add minecoins infuriating, or if they do exist they are impossible to find.

Could you please assist?

Thank you.