Hello we have a lot of sites with you, and we just added FB comments to some of them
But for some reason there is one that it’s not working on.
Would you be able to take a peek?
Thanks in advance for your help!
Hi There,
Please try going to Settings > Discussion > Allow people to post comments on new articles : Enable this option or edit post on upper right part look for Screen Options: Enable Discussion. Then Discussion tab will show like below and then Allow comments. 
Let us know how this goes.
That worked perfectly, thanks for all your help!
Glad to hear that. 