Trello and Slack : How do you add Trello onto a Slack channel that is private?

[Rene Ramirez]

I had to move all my Trello cards onto another Workspace due to the fact whoever made the board left the company. I want to add it into Slack on a private channel but it's showing that I'm unable. 

We were able to do so 5 years ago but we simply forgot how to do so. Please help.

[Carolina Lopez]

Hi Rene, welcome to the Atlassian Community!

You can link your Workspace to Slack on your Workspace settings:

After that, you can enable the Slack Power-Up to have the Slack icon on your cards:

If you have any error messages, please send a screenshot, and I'd be glad to help.

You can see more details about the Slack app here: https://support.atlassian.com/trello/docs/the-trello-app-for-slack/