Why Can’t I Add External Users to a Slack Channel?

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Overview

If you try to collaborate with someone outside your organization and receive a message indicating that only internal members can be added, it usually means there are restrictions in place at the workspace or channel level.

Cause

This issue typically arises due to Slack's security and privacy settings:

Only users within your internal Slack workspace can be added to certain channels, especially private channels.
Guests, external collaborators, or users from other workspaces—even if Slack Connect is enabled—cannot be added unless shared access is configured.
These limitations are often controlled by workspace administrators and apply more strictly to private channels.

Solution: Use Slack Connect

Slack Connect allows you to invite and collaborate with users from other organizations (e.g., clients, vendors, or partners) through shared channels.

Steps to Enable and Use Slack Connect

1. Check Admin Permissions

Ensure that Slack Connect is enabled in your workspace.
Admin approval is usually required during the initial setup or for new external connections.

2. Create or Share a Slack Connect Channel

Click the “+” icon next to Channels.
Choose “Create a channel” or open an existing one.
Enable the option: “Share outside your company.”
Enter the external collaborator’s email and send the invitation.

3. Approval Process

Admins from both organizations may need to approve the shared channel request.
The external user will receive an invite and must accept it.

4. Start Collaborating

Once all approvals are complete, the channel becomes a shared workspace between organizations.

Note: Slack Connect supports both public and private channels. You cannot manually add external users to an internal-only private channel unless Slack Connect is used.