Does not unlock content for already subscribed YouTube members

I have some restricted content that unlocks once a user subscribes to a YouTube channel and this works well enough for new subscribers. However, if a user is already subscribed to the channel and visits the page (or if I try to view that same page with the newly subscribed user signed into incognito), the plugin returns an error saying “Error occurred during the request. The subscription that you are trying to create already exists.”

How do I resolve this please? Is there an option that controls granting access for current subscribers or does anyone know a workaround?

Appreciate the help.

Kind regards.