When I add my payment method to my Apple ID it does not work.

What happens when you try? Error message(s)?

If necessary, contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

Apple on Twitter

If you add money to your Apple ID balance, It would take about 1 to 2 business days in order to process.

See -> Check your Apple ID balance

Check your Apple ID balance – Apple Support (UK)

You can also try to go to the iTunes Store, sign out, and then sign back in.