PromoRepublic allows you to connect 1 Facebook profile and the different Facebook pages and groups managed by this profile. If you have more than one Facebook profile, you may encounter the error "PromoRepublic account does not belong to this Facebook user"
Why the error? When you are scheduling your post; you're not logged into the Facebook profile connected to PromoRepublic. In order to solve this issue, log into the Facebook profile synchronised with PromoRepublic (in the same browser). Once it's done, retry the step.