Publishing on facebook failed

Almost exactly the same symptoms as in this thread:

https://premium.wpmudev.org/forums/topic/publishing-on-facebook-failed

I'd really appreciate some help here!

1. I have created apps all-over-again and granted permissions all-over-again and I persistently fail to auto post to the FB wall.

2. Mysterious issue with the dropdown showing just me and the app page and not my remaining pages (although it was showing all of them at some point).

3. I'm logged into facebook right through.

4. No conflicting social media plugins. No other FB plugins at all so far.

5. This is a multisite setup. I installed this plugin for a client on a single WP setup and it worked just fine for him. Now I'm jealous jealous!

I'd love to get some feedback on getting this up and running, thanks!