Grammarly accepts PayPal as a payment method as long as it is available in your region.
If you are having trouble getting Grammarly to bill through your PayPal account, PayPal can provide the most up-to-date information on the types of payment they accept for Grammarly transactions in your region.
If you need to update the payment method on your PayPal account, PayPal.com can help walk you through that process as well.
Note: Your Grammarly subscription must be managed on the Grammarly site to take effect, not on PayPal.com.