I know this is an old topic but I recently had this issue and the fix was to add the Outbound application to VVB admin and add the application trigger with the same dialed number pattern as the dial-peer on the egress gateway. In this case, we used the 7788000 given as the example in the StandaloneOutbound_Spec.doc that downloads with the original sample app. To start go to https://IPofYourVVBserver/appadmin/main
Also, make sure the IP address in the session target of the dial-peer on the egress gateway is the IP of your VVB server.
Hopefully this helps the next person searching for this failed, status ls_020 (ls_020) issue.