add_action( 'plugins_loaded', 'apple_pay_verification_file' );
function apple_pay_verification_file() {
   
    if ( $_SERVER["REQUEST_URI"] == "/.well-known/apple-developer-merchantid-domain-association.txt" ) {
      readfile( dirname( __FILE__ ) . "/apple-developer-merchantid-domain-association");
      exit();
    }
  }