.ics invitation calendar not working in outlook.co

Hi im using cakephp email to send an email with .ics calendar attached to it the problem is that the confirmation button si shown in yahoo and gmail prefectly but not in outlook.com. here's an example of an .ics file:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//T//T//EN
METHOD:REQUEST
BEGIN:VEVENT
UID:20150830T184133-19847-domain.com
DTSTAMP:20150830T184133
DTSTART:20150812T000000Z
DTEND:20150818T000000Z
ORGANIZER;CN=myteam:MAILTO:admin@myteam.org
ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN=brabrick@hotmail.com:MAILTO:brabrick@hotmail.com
LOCATION:new york
SUMMARY:Madrid
BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

here's my php code that's creating the appointement .ics file:

                $vcal = "BEGIN:VCALENDAR\r\n";
                $vcal .= "VERSION:2.0\r\n";
                $vcal .= "PRODID:-//T//T//EN\r\n";
                $vcal .= "METHOD:REQUEST\r\n";
                $vcal .= "BEGIN:VEVENT\r\n";


                $vcal .= "UID:".date('Ymd').'T'.date('His')."-".rand()."-domain.com\r\n";
                $vcal .= "DTSTAMP:".date('Ymd').'T'.date('His')."\r\n";
                $vcal .= "DTSTART:$visitedate\r\n";
                $vcal .= "DTEND:$visitedate\r\n";             
                $vcal       .=  "ORGANIZER;CN=myteam:MAILTO:admin@myteam.org\r\n";//j'ai ajouté cette ligne
                $vcal       .= "ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN=$mail[$iduser]:MAILTO:$mail[$iduser]\r\n";
                //$vcal .= "DTEND:$end\r\n";
                if ($loc != "") $vcal .= "LOCATION:$loc\r\n";
                $vcal .= "SUMMARY:$objet\r\n";
                $vcal .= "BEGIN:VALARM\r\n";
                $vcal .= "TRIGGER:-PT15M\r\n";
                $vcal .= "ACTION:DISPLAY\r\n";
                $vcal .= "DESCRIPTION:Reminder\r\n";
                $vcal .= "END:VALARM\r\n";
                $vcal .= "END:VEVENT\r\n";
                $vcal .= "END:VCALENDAR\r\n";


                $headers = "\r\nMIME-version: 1.0\r\nContent-Type: text/calendar; method=REQUEST; charset=\"iso-8859-1\"";
                $headers .= "\r\nContent-Disposition: attachment; filename=\"appointment.ics\"";
                $headers .= "\r\nContent-Transfer-Encoding: 7bit\r\nX-Mailer: Microsoft Office Outlook 12.0";


                $Email = new CakeEmail('smtp');
                $Email->to($mail);
                $Email->subject($objet);
                $Email->replyTo('admin@myteam.org');
                $Email->from ('admin@myteam.org');
                $Email->setHeaders(array($headers));

thanks in advance

Your ics file looks fine so the issue is most likely related to your email MIME structure. Have a look at Multipart email with text and calendar: Outlook doesn't recognize ics