MacOS 10.13.6 command line, MacOS Keybase client, and Android 8.1 client Facebook Proof is unreachable

I've followed the steps numerous times to try to prove my Facebook account on Android, the Mac client, as well as the Mac command line. All fail with this message after making the _public_ fb post:

`Error 500. Something is not right. We will look into it.`

I get that error on the `https://keybase.io/_/facebook_post_redirect?sig_id_med=...` url after making the fb post.

Link to public fb post here: https://www.facebook.com/Pyrrhusignius/posts/2316997828329536

I let it go for a few hours and then got this in an email:

`Hi, pyrrhusignius, your attempted facebook identity proof of pyrrhusignius never succeeded. We've been checking it repeatedly, and from our perspective, it's either (a) not there, or (b) not posted precisely.`

In between each attempt, I would delete the previous fb post and remove the Keybase app from my fb account settings here: https://www.facebook.com/settings?tab=applications

Start by reproducing the failure at the reported `https://keybase.io/_/facebook_post_redirect?sig_id_med=...` URL after creating a public Facebook post, using the Mac command-line, Mac client, and Android client paths mentioned. Trace the Facebook identity-proof flow and determine why the post is rejected; done means a valid public post completes proof without the Error 500 response.

Written by the indexing model from the issue text.