## Bug Description The Slack MCP plugin OAuth authorization always fails with the following error from Slack: > **为 Claude 授权时出错了。** > `redirect_uri did not match any configured URIs. Passed URI: http://localhost:3118/oauth/callback` ## Steps to Reproduce 1. Enable the Slack plugin in Claude Code (`plugin:slack:slack`) 2. Run `/mcp` and attempt to authenticate with Slack 3. Browser opens and redirects to the Slack OAuth authorization page 4. Slack immediately shows an authorization error

Slack MCP plugin OAuth fails: redirect_uri not registered in Slack app configuration

Resolved 💬 18 comments Opened Mar 23, 2026 by mhrong Closed May 30, 2026

💡 Likely answer: A maintainer (localden, collaborator) responded on this thread — see the highlighted reply below.

Bug Description

The Slack MCP plugin OAuth authorization always fails with the following error from Slack:

为 Claude 授权时出错了。 redirect_uri did not match any configured URIs. Passed URI: http://localhost:3118/oauth/callback

Steps to Reproduce

Enable the Slack plugin in Claude Code (plugin:slack:slack)
Run /mcp and attempt to authenticate with Slack
Browser opens and redirects to the Slack OAuth authorization page
Slack immediately shows an authorization error

Error Details

Slack OAuth app (client_id: 1601185624273.8899143856786) has not registered http://localhost:3118/oauth/callback as a valid redirect URI. This causes every authorization attempt to fail on Slack's side before any user interaction.

Screenshot of error:

The Slack OAuth page shows:

redirect_uri did not match any configured URIs. Passed URI: http://localhost:3118/oauth/callback

Environment

Claude Code version: 2.1.81
OS: macOS
Slack plugin config (~/.claude/plugins/cache/claude-plugins-official/slack/1.0.0/.mcp.json):

{
  "mcpServers": {
    "slack": {
      "type": "http",
      "url": "https://mcp.slack.com/mcp",
      "oauth": {
        "clientId": "1601185624273.8899143856786",
        "callbackPort": 3118
      }
    }
  }
}

Expected Behavior

OAuth authorization should complete successfully and Claude Code should receive a valid Slack token.

Actual Behavior

Slack rejects the OAuth request because http://localhost:3118/oauth/callback is not registered as an allowed redirect URI in the Slack app settings for client_id: 1601185624273.8899143856786.

Fix Required

The Slack OAuth app (client_id: 1601185624273.8899143856786) needs to have http://localhost:3118/oauth/callback added as an allowed redirect URI in the Slack API app configuration.

View original on GitHub ↗

18 Comments

IliaGolubenko · 3 months ago

Same issue here.

Claude Code 2.1.81, macOS
plugin:slack:slack via claude plugins install slack@claude-plugins-official
OAuth fails with: redirect_uri did not match any configured URIs. Passed URI: http://localhost:3118/callback
Reinstalling the plugin and retrying doesn't help — same port, same error every time.

The redirect URI http://localhost:3118/callback needs to be registered in the Slack OAuth app config for client_id: 1601185624273.8899143856786.

Rocker93 · 3 months ago

Same issue on Windows

orcaman · 3 months ago

Same issue for me

edda-o · 3 months ago

Same here - tried cleaning the cache and everything and nothing worked.

diegorv · 3 months ago

Same here

esetnik · 3 months ago

Same issue for me

abhishekpillai · 3 months ago

Looks like the issue is resolved. Works for me now.

hello-ashleyintech · 3 months ago

Hi all from the Slack Open Source team - this should be fixed now!

HolyNoodle · 3 months ago

Getting the error. Could connect last week. Now I have the same: redirect_uri did not match any configured URIs. Passed URI: http://localhost:3118/callback

Biswa-820 · 3 months ago

navs-github · 3 months ago

working for me as of now!

amitds1997 · 2 months ago

This does not seem to work for Claude Desktop which redirects to port 53280 and uses 127.0.0.1 instead of localhost. @hello-ashleyintech Is this something your team can help with or would the fix be needed at Claude Desktop's end?

ecktom · 2 months ago

There was a new version released for Cowork which allows adjusting the callbackPort.

Still Slack MCP cannot be connected using port 3118 since the host 127.0.0.1 does not seem to be whitelisted and 127.0.0.1 is hardcoded

dustinsmith1024 · 2 months ago

Stuck here as well. This would be a huge win for our CoWork 3p rollout.

ecktom · 2 months ago

Stuck here as well. This would be a huge win for our CoWork 3p rollout.

Yeah this is pretty frustrating considering how easy it would be to fix if only reaching the right person.
I already contacted both official Slack and Anthropic Support with 0 results (either stuck with the AI bot or a support engineer saying it's not in official scope and might arrive at some day).
@hello-ashleyintech, is this something you could help getting sorted out internally at Slack?

dustinsmith1024 · 2 months ago

I don't know when callbackHost got added but this is working for me now.

{
    "name": "slack",
    "url": "https://mcp.slack.com/mcp",
    "transport": "http",
    "oauth": {
      "clientId": "1601185624273.8899143856786",
      "callbackHost": "localhost",
      "callbackPort": 3118
    }
  },

mohamadsdg · 1 month ago

That error is from Slack's OAuth

Fix:

Go to https://api.slack.com/apps
Left sidebar → OAuth & Permissions
Under Redirect URLs, click Add New Redirect URL
Add: http://localhost:3118/callback
Click Save URLs
Retry the MCP connection in Claude Code

localden collaborator · 1 month ago

Thanks for the report. The Slack team fixed the redirect_uri issue server-side on March 23, and two commenters in this thread confirmed it working since. Closing as resolved.

For the separate 127.0.0.1 reports in May: those are Cowork/Desktop scope, not the Claude Code plugin. The workaround there is oauth.callbackHost: "localhost" per the May 13 comment. If that variant is still failing, please open a new issue against Cowork.