Pay With a Like - When someone has already "liked" content they can't re-like it

I'm using Pay With a Like on my fitness site. Users login into their free accounts and then have to like a page before their workout is revealed. This is great...

Except when they re-visit a page that they have already liked. The Pay With a Like remembers that they liked it so trying to re-like it doesn't work. I got it to work if I manually "unlike" the page and then re-like it. Unfortunately, I don't think people will figure this out on their own...I expect I'll get lots of emails about this problem when I make it active on my site.

Can I set it up so that once a person has liked a given page they will never have to re-like it in order to see that content?

If not, how else can I solve this problem?