It turns out that it was an even deeper billing issue than I initially thought. Somehow I had gotten my redeemed gift card to the point of it not being applicable until I attached a different card to my ID. So I did that and APPARENTLY it was trying to charge me again for the gift card I already paid for. I didnt know that until I put in my husbands card (because it wasn't accepting either of my cards) and then there was a charge on his account. This has NEVER happened to me when redeeming gift cards and I don’t know how it happened in the first place.
I bought the gift card.
Redeemed it.
No balance in iTunes.
I put the gift card in my “wallet”.
The full balance appears in iTunes.
I try to make the in-app purchase.
It says validation is required and that I need to update my billing information.
I do that, several attempts fail.
I get purchased declined emails from one of my cards.
Finally I use my husbands card.
Finally the validation goes through. (As well as another $26 and change charge for the gift card I already paid cash for in Walgreens).
So now the next step I think is to call Apple Support and have my husband call his bank to get this resolved. I’m so dumbfounded I could scream.