[BUG]

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Here's the exact text you can copy and paste:

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Title: Amazon Ads MCP OAuth fails with "Malformed Request uri"

Body:

Description

When attempting to connect the Amazon Ads MCP integration via the Claude web app, clicking "Connect" redirects to Amazon's OAuth endpoint which immediately returns:

{ "message": "Malformed Request uri" }

The failing URL is:

https://advertising-ai.amazon.com/authorize?response_type=code&client_id=[REDACTED]&redirect_uri=https%3A%2F...

Expected Behavior
Amazon OAuth consent screen should load, allowing the user to authorize access.

Suspected Cause
The redirect_uri parameter appears to be URL-encoded within an already-encoded query string (double-encoding). Amazon's endpoint rejects this as malformed.

Environment

• Claude web app (claude.ai)
• Browser: Chrome
• Amazon Ads account: active, US marketplace
• Note: SellerLabs MCP connected successfully with no issues using the same flow.

Screenshot
(attach your screenshot here)

---

Submit this at https://github.com/anthropics/claude-code/issues (or if there's a separate repo for Claude web app integrations, use that). Attach the screenshot you showed me.

What Should Happen?

Expected Behavior
Amazon OAuth consent screen should load, allowing the user to authorize access.

Error Messages/Logs

malformed request uri

Steps to Reproduce

Steps to Reproduce

1. Go to Claude web app → Settings → MCP Integrations
2. Find "Amazon Ads" MCP connector
3. Click "Connect"
4. Browser redirects to advertising-ai.amazon.com/authorize
5. Page displays { "message": "Malformed Request uri" }

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude Code version: 2.1.78

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

screenshots attached
This is working fine and we can connect into the Amazon Ads MCP via the PowerShell terminal on a windows machine. No luck using the claude wep app though.