Late update, but I see that the official doc hasn’t been updated.
So in case anyone ever runs into this issue:
If your monday app throws an “ Invalid redirect_uri ” error (after you’ve ensured that your redir_uri & board scopes are correctly configured):
Go to the server index.js file cloned from this git repo here & delete ‘/outh/callback/‘ that’s appended to redirect_uri in app.get('/start', (req, res) => {
This will send the user to the scopes page that’ll prompt them to authorize your app and then redirect them to /oauth/callback 