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Regarding the legacy PayPal plugin: PayPal Express Checkout has been deprecated, and as far as I know, you cannot set up a new PayPal merchant account which supports this integration method, which is why the plugin has been deprecated.
As such, we have recommended our users to switch to the Braintree APIs (which is now part of PayPal), to handle PayPal payment methods (the plugin stores the Billing Agreement ID, just like how it was done on Express Checkout, which allows for recurring payments).
If you have specific needs (e.g. need to support a legacy PayPal merchant account) and cannot use Braintree, please give us more details and we'll provide more specific guidance.