调用Monzo Auth API获取access token时遇client_id未知错误求助

Let’s walk through the most likely issues causing this error — I’ve seen this trip up a lot of Monzo API developers, so let’s break it down:

• You’re using the wrong ID entirely
  The GET /ping/whoami endpoint returns your user account ID, not the OAuth client_id required for the Auth API. You need to create a dedicated OAuth client in the Monzo Developer Console (under the "Clients" section) — that’s where you’ll get the valid client_id (and matching client_secret) for auth flows. This is the #1 mistake here, since the two IDs look similar but serve completely different purposes.

• Your parameter isn’t being passed in the correct format
  Monzo’s OAuth token endpoint (POST /oauth2/token) expects parameters to be sent as application/x-www-form-urlencoded (form data), not JSON. If you’re wrapping client_id in a JSON body or appending it to the URL query string, the API won’t recognize it. Here’s a correct example using curl:

  curl -X POST "https://api.monzo.com/oauth2/token" \
    -d "client_id=your_valid_oauth_client_id" \
    -d "client_secret=your_client_secret" \
    -d "grant_type=authorization_code" \
    -d "code=your_authorization_code" \
    -d "redirect_uri=https://your-redirect-uri.com"
  

• You’ve misspelled the parameter name
  Double-check that you’re using exactly client_id (lowercase, underscore included). Variants like clientId, ClientID, or client-id will be treated as unknown parameters by the API.

• You’re mixing environments
  If you’re testing in the Monzo Playground, make sure the client_id you’re using was created for the playground environment (not production). While the API base URL is often the same, mismatched environment credentials can still trigger validation errors.

Start with verifying your client_id source first — that’s almost certainly the issue if you pulled it from whoami. Once you have the correct OAuth client ID, double-check the request format and parameter spelling, and you should be good to go.

内容的提问来源于stack exchange，提问作者Wrumble