Invalid parameter value for redirect_uri: Missing scheme: /auth/google_auth_code/callback

I am trying to get an access and refresh token from Google from a authorization code for the server-side flow. I followed Google's guide here: https://developers.google.com/identity/sign-in/web/server-side-flow.

I am using using passport and passport-google-authcode.

Here are the routes for the node app:

router.get('/auth/google_auth_code',
    passport.authenticate('google_authcode', {
        scope:
        [
            'https://www.googleapis.com/auth/calendar',
            'profile',
            'https://www.googleapis.com/auth/userinfo.email'
        ]
    }),
    function () {
        res.end();
    })

router.get('/auth/google_auth_code/callback',
    passport.authenticate('google_authcode', {
        failureRedirect: '/error'
    }), 
    function (req, res) {
        // do something with req.user
        res.send('hello');
    }
);

Here is the passport config for this strategy.

passport.use('google_authcode', new GoogleAuthCodeStrategy({
    clientID: 'my client id',
    clientSecret: 'my secret',
    callbackURL: '/auth/google_auth_code/callback',
    // passReqToCallback: true
},
    function (accessToken, refreshToken, rawResponse, profile, done) {
            // unable to get here
    }
));

When an authentication request is made, Google responds with the following error:

{
  "error" : "invalid_request",
  "error_description" : "Invalid parameter value for redirect_uri: Missing scheme: /auth/google_auth_code/callback"
}

Here is my credential setup in the Google console:

At this point I don't know what else to do. I have also tried changing the callback URL in the passport.use to an absolute URL. I am definitely getting back a valid auth code (it looks like: 4/Mb2pcOyhYhziROyFHKH5pnzvUldYbAmMop9SJKbBHXQ). Let me know if there is any more relevant information that I can provide.

Thanks,
Sam

via SamB