They support credit/debit cards, bitcoin, and Paypal. I went with Namecheap especially because of their seamless payment method, Used to struggle at times paying for my domains with Gandi, etc.
Namecheap payment system works just fine.
You: "their billing works just fine" [then talking about payments, when I wasn't talking about payments but billing, "The process of sending an invoice (a bill) to customers for goods or services" -Wikipedia]
They have their billing for domains and products spread over several pages, there is not one place in the UI where they have all payments/billing combined, they don't have PDFs as I've stated and they don't sent invoices by email. Their billing UI is horrendous.