- App Version: 18.104.22.168
- Device: iPhone 5s (GSM)
- OS Version: Version 10.1.1 (Build 14B150)
As far as I know, you need some amount of rep on the site where you're trying to upload more than one image. I can find most convenient information only for Create Chat Rooms priviledge in the help:
What other new privileges in chat do I get?
At 100 reputation you also get access to the "Upload image" button in chat.
Probably information about restiction for uploading an image to the post absent due to overlook. But also my search engine could break.