Unable to purchase add-on with wallet funds

Hello,

I've got my child set up in Microsoft Family Safety. They want a Minecraft add-on that is $9. I put $10 in their wallet. When I approve the requested purchase in Family Safety, it says I need to add more funds. I have a screenshot of it showing both the $10 account balance (in my child's wallet) and the $9 price tag and the incomprehensible request to add more funds.

How do I approve this purchase?

I've spent a lot of time searching the incomplete or out-of-date instructions online. There is one set of instructions that claim to allow you to turn off the "Ask to buy" feature in Family Safety. However, the instructions don't match the actual interface and I can't find an "Ask to buy" feature anywhere.

I'd also appreciate directions on how to purchase a Minecraft add-on directly, for the exact amount it is worth, for my child. Having to put arbitrary amounts of money in their wallet is not acceptable to me. We'd buy more add-ons but I'm not willing to give Microsoft extra money through this scheme.

Thanks.