Q:

sort custom post by multiple meta key

I am trying to sort custom post data by meta key but only first Key is working, second meta key does not sort.
$args = array(
    'post_type' => 'mad_property',
    'post_status' => 'publish',
    'paged' => '-1',
    'meta_query' => array(
      'meta_query' => array(
        'relation' => 'or',
        array(
          'key' => 'sleeps',
          'value' => $_POST['sleeps'],
          'compare' => '=',
        ),
        array(
          'relation' => 'or',
          array(
            'key' => 'propertytown',
            'value' => $_POST['propertytown'],
            'compare' => '=',
          ),
        ),
      )

A:

https://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters
You should be able to copy the first example where it says Multiple Custom Field Handling
$args = array(
     'post_type'         => 'mad_property',
     'post_status'       => 'publish',
     'paged'             => '-1',
     'meta_query' => array(
         'meta_query' => array(
             'relation' => 'OR',
             array(
                 'key' => 'sleeps',
                 'value' => $_POST['sleeps'],
                 'compare' => '=',
             ),
             array(
                 'key' => 'propertytown',
                 'value' => $_POST['propertytown'],
                 'compare' => '=',
             ),
         ),
     ),
);

