Facebook thumbnail

Whenever I post a link to facebook, i cannot select a photo in that blog post. I tried using using the facebook debugger but this is what I see.

Errors that must be fixed
More Than One OG URL Specified Object at URL ‘https://singaporevegantriathlete.com/2014/03/10/review-afterglow/’ of type ‘article’ is invalid because it specifies multiple ‘og:url’ values: https://singaporevegantriathlete.com/2014/03/10/review-afterglow/, https://singaporevegantriathlete.com/2014/03/10/review-afterglow/.

Any help will be greatly appreciated.