Enabling the PayPal Subscription product feature is essential to the module's functions.

When you edit a product node, you should have a tab menu with 'Product', 'Attributes', 'Options', 'Adjustments', and 'Features'. Click on Features. Under the 'Add a new feature' menu, select 'PayPal Subscription' and click 'Add'. You should be presented with a page of options related to a PayPal subscription/recurring payment.

You can only use the URL shortcut link for products that already have this product feature enabled. The purpose of the URL link is to provide a way to create links/buttons directly to subscription payment on pages other than the product node.

I'm glad there's interest in this module, and I hope this discussion can help clarify how to use it.