Your payment method not valid in this store ?? What is the problem pliz

Based on that very meagre information all I can do is guess that the country that you are in is not the same as the country where your payment method is billed. The address in your Apple ID settings must match the the billing address on your credit card account, and both must be in the country whose iTunes & App Store you are signed in to.

I don't have a good answer, other than to get an credit card from a neighboring country and use that country's iTunes store. You might consider Egypt, which does have iPhone support. This is a general problem of using an iPhone in a country where Apple does not provide support.