Currently there are no other payment methods available. Circle is currently working on implementing other means of payment.All links you find when searching for “Integrating PayPal into or with Circle” describe third party solutions.
Products like Zapier, Memberstack, Memberful, Outseta and more. However, we are using the native Paywall function which is powered by Stripe. Stripe offers PayPal, however Circle has not implemented it in their Paywall service yet. And it is impossible for us to combine different platforms.