I cant add the money to an app.What i am suposed to do?

See if anything here helps.

Gift cards redeem.   *

Gift Card - can’t redeem.   *

Or if you aren't in Family Sharing.

Apple ID - Add funds to your ID      *

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   -

If necessary, try Twitter

https://twitter.com/AppleSupport.   -