Unfortunately, Slack does not (yet) support the ability to upload files into a Slack thread. But don't fret! We devised a way for BubbleIQ customers to be able to upload files into a thread so they are viewable in Slack and Zendesk. Here's how to do it!
In the thread of the ticket you want to upload a file, type "file-upload"
The bot will message you and ask you to upload a file in a direct message.
Upload your file, and the bot will delete the original message in the thread and paste a link to it in the thread.
The message will post to the thread as well as to Zendesk.
Here's a gif of the whole thing in action (with Rick and Morty for fun)