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.
I had a brief a phone appointment with Mr. Khanna this morning. He was very friendly, understanding, and patient about hearing my situation regarding permanent residency. I found his advice to be excellent. Also, I found his team to be very responsive, efficient, and thoroughly professional.