<?php

if($isError1) {
    header("HTTP/1.1 415 Unsupported Media Type");
    trigger_error("HTTP/1.1 415 Unsupported Media Type", E_USER_ERROR);
    exit;
}

// do sth if not

if($isError2) {
    header("HTTP/1.1 415 Unsupported Media Type");
    trigger_error("HTTP/1.1 415 Unsupported Media Type", E_USER_ERROR);
    exit;
}

// continue action