/oauth2/token route is returning a binary in response

Hi, i'm having problems when deploying my integration to my QA environment, i have already tested it in development and everything was right but i'm getting a totally different response in the route /oauth2/token then what i was receiving during my tests.
The app environments are the same and the code too, so i'm lost over here, any answer could come handy!

Here is how i start my OAUTH flow:
The client will call this route witch should redirect the client to Dropbox authorization page:

 

    async get(req, res) {
        const usuario = await Usuario.findByPk(req.params.usuario_id);

        return res.redirect(
            `https://www.dropbox.com/oauth2/authorize?client_id=${process.env['APP_KEY']}&response_type=code&redirect_uri=${process.env.DROPBOX_WEBHOOK_URL}&token_access_type=offline&state=unidade_id:${usuario.unidade_id}`
        );
    }

 

After the user authorizing my app the code bellow is called witch is the code for the route provided in the redirect_uri query param:

 

    async index(req, res) {
        const params = new URLSearchParams();
        params.append('code', req.query.code);
        params.append('client_id', process.env['APP_KEY']);
        params.append('client_secret', process.env['APP_SECRET']);
        params.append('grant_type', 'authorization_code');

        params.append('redirect_uri', process.env.DROPBOX_WEBHOOK_URL);

        const fronURLRedirect = new URL(
            '/dropbox',
            process.env['APP_FRONT_URL']
        );
        try {
            const { data } = await axios.post(
                process.env['DROPBOX_OAUTH2_TOKEN_ROUTE'],
                params
            );

            const [_, unidade_id] = req.query.state.split(':');

            await AcessoDropbox.create({
                ...data,
                update_token_date: new Date(),
                unidade_id,
            });

            fronURLRedirect.pathname = '/dropbox/sucesso';
            return res.redirect(fronURLRedirect.href);
        } catch (error) {
            console.log(error);

            fronURLRedirect.pathname = '/dropbox/erro';
            return res.redirect(fronURLRedirect.href);
        }
    }

 

And after that our app is successfully authorized, at least during development, here is the return value that i receive from my POST call in the code above in development:

And here is an example of what i receive back in QA with the same code, same app key and secret, the only difference is the redirect_uri:

Here is a full print of my debugging:

I'm also receiving the query params as it should:

It looks like i'm receiving a binary as a response witch is totally different from what i was receiving during my tests, i searched the docs and did some googling but no luck!

My Dropbox app isn't applied to production, i'm wondering if that's the problem.