when i try to pay by alertpay this message appear to me Due to temporary difficulties we cannot process MasterCard/Visa transactions at this time. Please try again later, or use an American Express card
Yes, there is a problem with paying through AlertPay - It is already known. Dave is on the verge of fixing it soon.
You could try instead to pay using an American Express Card instead - since that should work judging by the error message.
Or you can rack up 250+ posts and pay through PayPal... Those are your own Payment Methods. AlertPay is down for some people... So those are the only alternatives. It'll be fixed soon, don't worry.