What this error means

Streamable HTTP error: Error POSTing to endpoint: unauthorized: not authorized to use this Copilot feature (code: 403) is a Claude Code failure pattern reported for developers trying to fix github mcp authentication failure on claude code web caused by copilot entitlement check failing, resulting in 403 and misleading oauth redirect to google drive. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #59953 opened May 17 2026. Root cause identified as account/org Copilot feature entitlement, not transient outage. OAuth flow triggered as wrong recovery path produces misleading 'Server Turned Down → Google Drive' page. High commercial value — blocks GitHub integration in paid Claude Code web sessions. Category mapped to AI Coding Tools per SKILL.md rules.

Common causes

  • GitHub issue #59953 opened May 17 2026. Root cause identified as account/org Copilot feature entitlement, not transient outage. OAuth flow triggered as wrong recovery path produces misleading 'Server Turned Down → Google Drive' page. High commercial value — blocks GitHub integration in paid Claude Code web sessions. Category mapped to AI Coding Tools per SKILL.md rules.

Quick fixes

  1. Confirm the exact error signature matches Streamable HTTP error: Error POSTing to endpoint: unauthorized: not authorized to use this Copilot feature (code: 403).
  2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
  3. Verify the account session, API key, provider settings, and environment where the failing tool is running.

Platform/tool-specific checks

  • Verify the command, editor, extension, or API client that produced the error.
  • Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
  • Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

  1. Capture the exact error message and the command, editor action, or request that triggered it.
  2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
  3. Review the source evidence below and compare it with your environment.
  4. Apply one change at a time and rerun the smallest failing action.
  5. Keep the working fix documented for the team or deployment environment.

How to prevent it

  • Keep provider/tool configuration documented.
  • Record non-secret diagnostics such as tool version, provider name, model name, and command path.
  • Add a lightweight check before CI or production workflows depend on the tool.