I know this issue has to do bit more with SIP and off from kamailio problems, but just wanted to know your opinions on this.

I have my sip extensions registered to kamilio and Asterisk works as a voicemail server.

Now to implement MWI i send NOTIFY packet from Asterisk to Kamailio and from kamailio to SIP extension (Grandstream GXP2000).

here is the packet that travels from kamailio to extension and the response sent from extension to kamilio.

===========================

NOTIFY sip:1111111@arzoo.com SIP/2.0
Max-Forwards: 10
Record-Route: <sip:172.18.100.74;lr;nat=yes>
Via: SIP/2.0/UDP 172.18.100.74;branch=z9hG4bK3c3.e1003f03.0
Via: SIP/2.0/UDP 127.0.0.1:45382;received=172.18.100.73;branch=z9hG4bK.4f83530d;rport=45382;alias
Via: SIP/2.0/UDP 172.18.100.73:5060
From: <sip:111@arzoo.com>
To: <sip:1111111@arzoo.com>
Contact: <sip:1111111@arzoo.com>
Call-ID: 4d61cf9e505d40e905032a18329d61ec@172.19.100.42
CSeq: 1 NOTIFY
User-Agent: VoiceMail
Event: message-summary
Content-Type: application/simple-message-summary
Content-Length: 39

===========================

SIP/2.0 415 Unacceptable Content-Type
Via: SIP/2.0/UDP 172.18.100.74;branch=z9hG4bK3c3.02003f03.0
Via: SIP/2.0/UDP 127.0.0.1:43416;received=172.18.100.73;branch=z9hG4bK.7be73901;rport=43416;alias
Via: SIP/2.0/UDP 172.18.100.73:5060
Record-Route: <sip:172.18.100.74;lr;nat=yes>
From: <sip:111@arzoo.com>
To: <sip:1111111@arzoo.com>;tag=3c6ba3e4a93d6864
Call-ID: 4d61cf9e505d40e905032a18329d61ec@172.19.100.42
CSeq: 1 NOTIFY
User-Agent: Grandstream GXP2000 1.1.4.14
Accept: application/sdp, application/simple-message-summary, application/octet-stream, application/dialog-info+xml, application/pidf+xml, message/sipfrag;version=2.0
Content-Length: 0

===========================

Please guide me in right direction to get rid of 'Unacceptable Content-Type' problem.