Wrong email/password

I am using my own database and only want to use Auth0 for allowing users to login. Do not want to migrate my users here also. So for this I am trying to write a login script but it always returns “Wrong email or password”
My login script is like this :

function login(email, password, callback) {
  	const requestPromise = require('request-promise-native');
	const options = {
        uri: 'http://**.**.**.**/vendor/login_vendor',
        json: true,
        method: 'POST',
        body: {
            "username": some_user_name,
            "password": user_password

    let vendor_token = undefined;
    await requestPromise(options)
                        .then((body) => {
                            vendor_token = body.token;
                        .catch(err => {
                            vendor_token = 0;
                            // console.log(err);
  	const msg = 'Please implement the Login script for this database connection ' +
    	'at https://manage.auth0.com/#/connections/database';
  	return callback(new Error(msg));

And I know that username/password is not wrong, also that api call I am making works fine on Postman

Also to add the api to which I am calling returns on successful login

    "success" : true,
    "token" : "Bearer ****........*****",
    "id" : ******

for invalid username :

    "username": "username not found"

for wrong password :

    "password": "password Incurrect"