MessageSend send FAILURE over OpneVpn

Hello everyone,
I’m having hard time fixing a problem regarding sending SIP message with MessageSend()

I have configured asterisk as a simple gsm gatway, the server is connected to my home router via Wifi with a static IP 192.168.1.222
All is working fine when i connect to asterisk from sophtphone in the local network.

in order to have remote acces i installed OpenVpn server in the same machine, now i can connect to asterisk from the internet using vpn and i can make and recive calls, however, i get a FAILURE from the MessageSend(sip:200,asterisk) (200 is the username for the sip account).

I tried to use

MessageSend(sip:200@10.8.0.2,asterisk) 
MessageSend(sip:10.8.0.2,asterisk)

where 10.8.0.2 is the vpn Ip of the softphone, i get SUCCESS as Message send status but the message is not delevred to the sip client.

can someone help me fix this issue

Does the softphone / sip client advertise basic support for SIP MESSAGE per RFC 3428 but then drop the message instead of display it ? Are you able to send and receive messages between two separate devices directly on a test LAN ?

Also per the sip: you might consider upgrading to newer version of Asterisk using PJSIP and the corresponding pjsip: technology.

Related there is RFC 8591 out of draft since April 2019. The Abstract concludes with:

“It updates and provides clarifications for RFCs 3261, 3428, and 4975.”

Any of those could be related to MessageSend() interactions; it depends on softphone / sip client implementation.