We display Stripe's credit card subscription form on the upgrade page, and they do the job. All credit card information is stored on Stripe's servers securely. We do not see credit card details during or after the payments.
You can see Stripe’s logo lower-left corner on the upgrade page.
We're planning to add PayPal's subscription system as an alternative payment method in 2021 Q4 for our users who would like to use PayPal.