We get this question a few times every year. The answer is simple. When you sign up for a merchant account you write on the application what your average charges are. When the underwriting team lets your account go thru its only for those amounts. Sudden increases in the amount being charged or one large amount are suspicious. The company is afraid that it isn't really a donation or payment. If its a loan its against the merchant terms and your account can be closed completely.
So before you want to charge a large transaction request approval before charging. They will need proof that it is a donation or payment and not a loan etc. Charging without approval can make all your funds delayed fro up to 6 months.