Thanks for the quick reply! I'm trying to establish a policy-based VPN where one side has a dynamic IP. All of the documentation for site-to-site VPNs seem to require static IPs. For example (https://www.juniper.net/documentation/en_US/junos/topics/topic-map/security-policy-based-ipsec-vpns.html).
I assume that the SRX is waiting for traffic to establish the IPSec tunnel per the config: set security ipsec vpn Dynamic-VPN establish-tunnels on-traffic. Attempting to change to immediately throws a commit error.