Hi @olilemire, welcome to our Community!
Can you walk me through the steps that you follow, when trying to share content to Slack, please?
Also, if you could follow the steps mentioned at this Help Center article, in order to connect Slack directly to Dropbox, that'd be amazing.
Keep in mind that it mentions, that if you can't see Slack on the App Center menu, you can use the App Center search bar.
Let me know more, and we'll take it from there!