使用RRule插件在fullcalendar V4中输出事件（json）

This is the PHP code that loads the events :

$q_e = mysqli_query($sqllink,"SELECT * FROM data_calendar_event WHERE
nuid='$nuid' AND valid='1'");
while ($r_e = mysqli_fetch_array($q_e) ){

    $start  = date("Y-m-d H:i",$r_e['StartDate']);
        $end    = date("Y-m-d H:i",$r_e['EndDate']);

    switch($r_e['FullDay']){
        case 0:
            $FullDay = FALSE;
        break;

        case 1:
            $FullDay    = TRUE;
            $end        = NULL;
        break;
    }
    //$rrule = "DTSTART:20129201T103000Z
RRULE:FREQ=WEEKLY;INTERVAL=5;UNTIL=20120601;BYDAY=MO,FR";// NULL;
    $EventID = base64url_encode($r_e['EventID']);
    $event_array[] = array(
    'id'                => $EventID,
    'title'             => $r_e['EventName'],
    'color'             => $r_e['EventColor'],
    'allDay'            => $FullDay,
    'start'             => $start,
    'end'               => $end,
    //'rrule'           => $rrule
    );
}

This is the javascript that calls the PHP script :

eventSources: [{
          url: 'load.events.php',
          method: 'POST',
          extraParams: {
            token: '<? echo $token; ?>'
          },
        }],

the token is just an internal part of the script.

Rrule output is something like this : DTSTART:20190301T230000Z RRULE:FREQ=WEEKLY;INTERVAL=1;BYDAY=MO,WE,FR;COUNT=5

I am using the RRule Plugin of Fullcalendar and if I uncomment rrule I get the following error : Failure parsing JSON Object.

I have looked into the docs at https://fullcalendar.io/docs/rrule-plugin and followed the instructions, but I must have missed something.