Do I have to use Stripe, or can I just take bank transfers?

You don't have to use any single rail. Manual bank transfer is fully supported: you share your bank details on the invoice, the client transfers the money, and you confirm receipt — at which point the invoice reconciles.

It's the simplest option and involves no payment gateway, though it relies on you to mark the payment received rather than it clearing automatically. Many people pair it with one online rail so clients can choose the speed of cards or UPI when they want it.