Apple gift card won't let me make an in-app purchase

I'm trying to buy an in-app currency with my iTunes gift card (which is now like less than $3), but when I attempt to purchase the currency, it sends me to "Verification Required- Before you can make purchases you must go to Settings > iTunes & App Store > Apple ID and verify your payment information." After hitting 'continue' under the pop-up, it sends me to the Manage Payments page, which shows my $3. If I press on the gift card, my only other option is to add another gift card, or add funds. It's acting as if I don't own the $3, and it'd be a shame if I can't use the rest of it.