You have to pay when you apply for an American school online, that is, you have to pay at the same time when you finally submit the documents, so that the submission can be successful.

the way to pay online is to enter the details of the credit card, and the school will deduct the money immediately.

If you don't trust the intermediary, you can do it yourself when you pay. At your home or the intermediary, you can immediately see whether the payment is successful.