To publish a post on a page you should do the following steps:
Select “Add account” -> Facebook
A window will appear which offers to grant the rights to the app to access the profile name and picture. Press Continue.
If you have already granted all the rights to the app, you will be automatically redirected to step 4.
Important!
Only managers or editors can link Facebook pages to the Service.
If, for some reason, you cannot see any page you need, check if you have the relevant rights to this Facebook page.
You also need to have the administrator or editor rights to a page to make posts. If posts are not published, make sure that the above-mentioned rights to the page are granted to the Facebook user.