This is a major bug fix for uploading attachments - you will need to upgrade to upload attachment blocks.
Many thanks to @jkap (seriously, thank u for being ok with not only reverse engineering your API, but also helping me out a bunch) and all the others in this GitHub thread for the fix!
as always you can install cohost.py with pip install cohost - enjoy chosting!
⚠️ Heads up! 
Cohost.py is still experimental, etc etc etc... you get the picture. Please submit bugs, feature requests and PRs to the GitHub repo!
🔺 Danger! 
If you're making a bot, please honor @jkap's little notes on bots! And, as always, don't make this site awful :)
check out the source for this post
ps: feature requests, bug reports and PRs? super welcome. check out our github. pybug is waiting.
quick edit: in future, I'll post all status announcements to @cohost-py - this is so I can follow Good Guidance(TM) and have 2FA on my main account, and have a second account for bot posting. you should do the same!
i'll still reblog status announcements, but, hey, if you Just want release notes that's the place to go