Changing email status when the product is purchased

Hi guys,
I am selling an e-book. Advertising through FB.
However, now and then, I have the client in the system which has the email status on unsubscribed or non-engaged - unsubscribed.
Is there a way to set them on subscribed to deliver the content.
I am not using the Infusionsoft merchant account.
I do use Plusthis but Easy opt-in doesn’t work.

I care about my list cleanness, but I don’t want to check every single purchase manually to see if they are new clients or the old ones.