Getting $_POST empty in AJAX callback
Try something like this:

$.ajax({
   url: Drupal.settings.property_check.base_url + '/search/property-by-address',
   type: 'POST',
   data: {
       'add1':'address line1',
       'add2':'address line2',
       'add3':'address line3'
   },
   headers:{
       'Content-Type': undefined,
   }
}).done(function(response) {
        console.log(response);
})


or

 var address = {'add1':'address line1','add2':'address line2','add3':'address line3'};

 $.ajax({
     url: Drupal.settings.property_check.base_url + '/search/property-by-address',
     type: 'POST',
     data: address,
     headers:{
         'Content-Type': undefined,
     }
 }).done(function(response) {
     console.log(response);
 })