GinaVF, I have this problem too.
Firstly, Apple Photos is like iTunes - they're both databases. Each photo is a blob inside the database, so it is invisible to the file system. Facebook etc can only see the files in the file system. It cannot see inside the database of photos, so it can't find anything.
Apple Photos will only help you send a photo to your own Facebook page, using the icon that looks like a box with an arrow pointing up.
However, as you found, it cannot send a photo to a Facebook page that is not your own.
The work-around is to EXPORT the photo you need from Apple Photos to a file folder like "Desktop". This creates a separate file for the picture, and Facebook can see that file. Using Facebook, you can then import that file.
11-10-2017 10:59 PM