Use one gift card in two accounts.

There is not a way to split payment between two credit cards. what you can do is purchase a xbox gift card with one of the credit cards put that xbox gift card onto the account then you would be able to split the payment between the gift card balance choose
this first as the first option that you want to use to pay then it will ask you how you want to pay the difference and then you can use the other credit card.

Hello, first it's a pleasure to be able to help you today.

My name is welcome to the community and Merry Christmas.

Hello Shamzz345, by your description if you have two account balance information showing in your Microsoft account but both are in dollars, that means one must be US dollars and one is probably Canadian dollars, the system makes that distinction with Gift Cards.

Try to check in the purchase description of the card you bought from Amazon which region the Gift Card you bought belongs to.

Hello, first it's a pleasure to be able to help you today.

My name is welcome to the community and Merry Christmas.

Hello ISAGWEN, by your description if you have two account balance information showing in your Microsoft account but both are in dollars, that means one must be US dollars and one is probably Canadian dollars or other country do use dollars, the system makes that distinction with Gift Cards.

Try to check in the purchase description of the card you bought from Wallmart which region the Gift Card you bought belongs to.

Gift cards cannot be used to purchase gift cards. The Microsoft account balance is essentially the same as a gift card since funds typically come from Xbox gift cards.

Would like transfer fund into my grandson Microsoft account, it not family account.

Hello, you are unable to transfer the funds directly to your grandson. You may however purchase a digital gift card that will provide a code that can be redeemed on the Microsoft Store, directly from your grandson's Xbox. I have provided two links. One in
which you can purchase the digital gift card, and another that shows how to redeem codes.

Digital Gift Card

https://www.microsoft.com/en-us/p/microsoft-gift-card-digital-code/cfq7ttc0k61w

Redeem Codes

https://support-origin.xbox.com/es-EC/billing/prepaid-codes/redeem-prepaid-codes