https://support.wix.com/en/article/request-paypal-pro-integration-in-wix-stores
https://support.wix.com/en/article/request-using-paypal-plus-as-a-payment-provider
Although you can see if you can connect via Paypal’s own REST API.
https://developer.paypal.com/docs/api/overview/
https://developer.paypal.com/docs/
https://developer.paypal.com/docs/classic/products/payflow/
There is a Wix example for using Stripe which you can have a look at and get the general idea of how to do it though code.
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-stripe-payment-processing