jQuery AJAX url wit variable

try with Axios instead jQuery and check the response, example

let form_data = new FormData;
form_data.append('action', 'myAction');
form_data.append('first_name', 'my first name');

axios.post(myVars.ajax_url, form_data).then(function(response){
  console.log('response', response.data);
}).cath(console.log)