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These errors apply to every MCP client. For an error specific to your client, see its page: Claude Code, Cursor, VS Code, Codex or Gemini CLI.

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The server does not appear in your client

Check the JSON syntax of the configuration file: a trailing comma breaks the whole file. Restart the client, and run npx -y @nuntly/sdk-mcp@2 in a terminal. It prints NUNTLY_API_KEY environment variable is required. or waits silently: both mean the command resolves. Press Ctrl+C to stop it.

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NUNTLY_API_KEY environment variable is required. at startup

The server reads the key from the env of its client configuration. Put it there.

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command not found: npx or The term 'npx' is not recognized

The first message comes from bash, the second from PowerShell. Install the current LTS release of Node.js from nodejs.org.

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A tool returns isError: true

The result text gives the HTTP status, the error title and the request id. Give the request id to support.
  • A 401 titled Onboarding emails can only be sent to the organization owner means the recipient is not your account address. Any other 401 means the key is wrong, revoked or mistyped.
  • A 403 that names a domain means the key is restricted to other domains: clear Restrict to domains on the key.
  • A 403 that says the organization is not active means it cannot send: contact support.
  • Any other 403 means the key lacks the permission, for example a Sending only key on a tool that reads or manages resources.

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A tool rejects an argument

The server refuses an argument the tool does not declare and sends no request. Use the argument names that tools/list returns, for example scheduledAt.