gift card use

I have $50 on my account iTunes will not let me use without putting in a credit card.

That $50 is on your Apple ID balance.

See -> Check your gift card balance

Check your gift card balance - Apple Support

or See -> Check your Apple ID balance

Check your Apple ID balance – Apple Support (UK)

See -> Change, add or remove Apple ID payment methods

Change, add or remove Apple ID payment methods – Apple Support (UK)

• and set your Apple ID balance as your default payment.

If you update your payment method or add funds to your Apple ID balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.