$member_details->user_login = array_map( 'sanitize_text_field', $_POST['user_login'] );
$member_details->user_role = array_map( 'sanitize_text_field', $_POST['user_role'] );
$member_details->status = array_map( 'sanitize_text_field', $_POST['status'] );

$member_details_encode = wp_json_encode( $member_details );

  global $wpdb;

  $member_result = $wpdb->insert( 'wpxa_project_members',

         array(

              'project_id'     => $_SESSION['project_id'],
              'author_id'      => $post_author,
              'member_details' => $member_details_encode

              ),

         array(

              '%d',
              '%d',
              '%s'

      )

    );

wp_mail($to = $post_author, $subject = 'This is the subject', $message = 'This is the message');