How do I make slash commands work on my bot in Slack?
I'm using chat.postMessage to have the bot post.
For example, if I type /giphy something, it pulls in a GIF image, but if my bot posts the exact same thing it does not do anything.
It seems like you won't be able to do what you're trying to do. As far as I can tell you can't have one Slack Integration trigger another Integration. It's not hard to replicate the functionality of the /giphy Integration, though.