Slack treats apps differently than users. The way you can invite human users to channels is slightly different from the way you can add apps.
Method 1: Use the /invite command
Copy-paste the exact command "/invite @paco" without the quotes for this method to work.
Method 2: Mention @Paco in a message
If you write @paco in a channel and try to send a message, Slack will automatically prompt you to add Paco to the channel
Once Paco is added to the channel, you will see a confirmation message
Do you still experience any Paco setup issues? Please reach out to the Paco Support Team!