USCIS Guidance on Payment of N-400 Application Fee with a Credit Card
You may pay for your N-400, Application for Naturalization, using a credit card. There is no additional fee to pay with your credit card. The N-400 is the only form that can be paid for by credit card using the G-1450, Authorization for Credit Card Transaction.
Acceptable Credit Cards
You may use Visa, MasterCard, American Express and Discover. You may also use gift cards with Visa, MasterCard, American Express and Discover logos.
My wife and I got our Green Cards through the Law Offices of Rajiv S Khanna. Every single employee who handled our files starting with the Labor Certification through the I-140 process and the I-485 application was a pleasure to work with and was extremely professional and helpful. I can definitely see why 'The Law Offices of Rajiv S Khanna' has such a great (and well deserved) reputation across the US.