why do i get a 400 bad request error code example

Example: error: request failed with status code 400

You should add a catch to the get call:

import axios from 'axios';
import config from './config';

axios.get('${config.serverUrl/api/contests')
  .then(resp=>{
    console.log(resp.data);
  })  
  .catch(error=>{

  });