Whenever I call someone, Incompatible SDP comes up. I've already read the other thread on incompatible SDP but it still didn't help.
If possible, please try from a different data network. Chances are that it's a NAT traversal issue when sending the media once the call is setup. It's a relatively infrequent issue with WebRTC but occasionally happens.
Would using a vpn work?
Not really sure, but doubtful. Give it a shot, and let us know if it makes a difference.
VPN will work when you disable ipv6 of your WLAN Networkadapter and when vpn has ipv6 address.