How do I integrate PayPal Express Checkout with Paid Membership Pro?
Purchase, download and install the Paid Memberships Pro module, then follow their instructions for integration, available in their article How to enable Express Checkout.
Note: Additional modules are available to add subscription support to your WooCommerce shopping cart. PayPal recommends that you do research before purchasing any modules to ensure those modules will support the feature sets you want. To ensure a safe recovery path in case you need one, always back up your site before installing any modules.
Paid Memberships Pro Support