CAUTION: provisional header are shown [duplicate]

Answer 1

Your problem may be the header() coming after the ob_start() function. Try to put the header() before starting the buffer like so:

header("Content-Type: application/json");
header("Cache-Control: no-cache, must-revalidate");
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT");
ob_start();