As the U.S. Citizenship and Immigration Services (USCIS) previously announced, USCIS will only accept electronic payments for paper-filed forms. Payments may be made either via credit card or debit card using Form G-1450, Authorization for Credit Card Transactions, or ACH debit transactions from a U.S. bank account using Form G-1650, Authorization for ACH transactions.
By requiring electronic payment, USCIS notes that it eliminates the need for benefit requestors and third-party payors to bring funds into field offices.
More details can be found on the USCIS site
here.