400 bad request when try to get the access token

[BagaJing]

I am just writing to get the access token in node js.

When i try to get the access token with the following code with 'fitbit-client-oauth2', the page always reflect 400 bad request.

I try other method to get the access token, it reflect the same error.

Please help. thanks.

    app.get('/auth/fitbit/callback', function(req, res, next) {
    
        var code = req.query.code;
        
        client.getToken(code, redirect_uri)
            .then(function(token) {

                // ... save your token on db or session... 
                
                // then redirect
                res.redirect(302, '/user');

            })
            .catch(function(err) {
                // something went wrong.
                res.send(500, err);
            
            });
    
    });
app.listen(3000);

err response:

{"errors":[{"errorType":"invalid_request","message":"Missing parameters: code Visit https://dev.fitbit.com/docs/oauth2 for more information 
on the Fitbit Web API authorization process."}],"success":false}