VPN - Fortinet - Problem with connection

SFOS: 5.0.0.67

Mobile Network → Data access point → Protocol = IP

In VPN advance settings, Port is configured, Disable IPv6 enabled, Allow self-signed certificate enabled(this Fortigate use factory default cert).

I can ping and telnet Fortigate IP/port from CLI.(curl -v telnet://fortigate.ip:port says connected).

When VPN connection is activated, SFOS displays “Problem with connection” and “Idle” in a loop, and never connects. I have ran debug on Fortigate device and it never receives SSL-VPN connection packet from SFOS.

Any help in getting this work is highly appreciated. Thanks.