Q: Why can't I buy gems in clash royale?

Hi

As the message advises, contact iTunes Support (where you have posted is not iTunes Support - it is a user-based community):

https://www.apple.com/support/itunes/contact/

WE need an answer plz ??

Answer for what ? If you are getting a message to contact iTunes Support then have you done that ? We are fellow users, these are user-to-user forums, we won't know why you are getting a message to contact Support

please tell me

If you are getting a message to contact iTunes Support that is what you need to do

Please do exactly as the message suggests and contact iTunes support at the included link.