Hi @renzodangelo,
If you sell subscriptions exclusively with PayPal Payments then the best thing, for now, would be to disable the guest checkout option in WooCommerce so that only registered users can visit the checkout page.
We understand that this is not the flow most store owners are looking for, but currently, this is the best method to ensure that the subscription will continue to renew properly.
A plugin like this can improve the WooCommerce behavior around this a bit to display a registration form instead of an empty page when attempting to view the checkout.
When the user is logged in, then the gateway will be loaded and subscription purchases should be successful.
With the older version 1.6.1 and before, guest users could also purchase subscription products, but saving the payment method may fail without any obvious errors. This wouldn’t cause any problems until the first renewal would take place and fail due to no saved payment method.
Restoring the guest checkout for subscriptions is one of our top priorities and we hope to have a solution ready for sometime in January. We are working on quite a few Vaulting related improvements to provide a more consistent experience.
If anything remains unclear, please create a separate thread here in the support forums for us to look into further. Thanks!
Kind regards,
Niklas