in the # set security setting
is vSRX support dynamic-vpn ??
in the screen cap left is SRX300 , right is vSRX
This change is since 15.1X49-D80.
Refer release notes: https://www.juniper.net/documentation/en_US/junos/information-products/topic-collections/release-notes/15.1x49-d80/index.html
Refer the VPN sub section under "New and Changed Features" and "changes in behavior and syntax" sections.