"Failed to add marketplace: Failed to fetch git marketplace from the provided URL." when adding private marketplace hosted on non-GitHub Git host

[rameier]

Describe the bug

Description

Adding a private Agent Plugin Marketplace hosted on a self-hosted GitLab instance works correctly in GitHub Copilot in VS Code but fails in Copilot CLI with the error:

**Failed to add marketplace: Failed to fetch git marketplace from the provided URL. Please verify that the URL and reference are correct. **

Affected version

GitHub Copilot CLI 1.0.12.

Steps to reproduce the behavior

1. Host a valid plugin marketplace (with a marketplace.json at the repository root and with a marketplace.json unter .github/plugin) on a private, self-hosted GitLab instance (e.g. gitlab.example.com/org/my-marketplace).
2. In VS Code — Open Copilot Chat → Settings (⚙) → Plugins → Browse Marketplace (+) → Enter the Git URL of the private marketplace → Confirm.
   • Result: The marketplace is fetched successfully, and its plugins are listed and installable. ✅
3. In Copilot CLI — Run:

   copilot plugin marketplace add gitlab.example.com/org/my-marketplace

   • Result: Error — Failed to add marketplace: Failed to fetch git marketplace from the provided URL. Please verify that the URL and reference are correct. ❌

Expected behavior

The CLI should be able to add and fetch a private marketplace from a non-GitHub Git host, the same way VS Code does. If authentication is required, the CLI should prompt for credentials or reuse existing Git credentials.

Additional context

Environment

• OS: Windows
• Copilot CLI version: (latest as of 2026-03-30)
• VS Code version: (latest as of 2026-03-30)
• Git host: Self-hosted GitLab (private repository)
• marketplace.json location: Repository root (also tried .github/plugin/)

Additional Context

• The marketplace.json is valid and follows the documented schema. VS Code successfully parses and displays the plugins from the same repository.
• The repository is accessible via Git (clone works with proper credentials).
• It appears the CLI may not be handling authentication for non-GitHub Git hosts, or may not be looking for the marketplace.json in the same locations that VS Code checks (root vs. .github/plugin/).
• This could also be related to the CLI only supporting github.com as a marketplace provider and not supporting arbitrary Git hosts.