How can I solve "Your Purchase could not be completed" in Hay Day

When I purchase diamond in Hay Day, I got this message: "Your purchase could not be completed" , then "cannot connect to itune store". I had this problem before but then it was solved. Now I've got it again, but I don't know exactly how to fix it right away. Can anyone help me? I'm pretty sure that my account is ok with master card provided.