You need a rule like that on the secondary for the initial sync. When that sync happens the rule on the sync interface on the Primary will sync to that interface so it also needs to be in place.
If the rule is on the sync interface on the primary and you end up with nothing on the sync interface on the secondary you likely have an interface mismatch.
Use Status > Interfaces on both to be sure they match. Everything on every interface has to match exactly
Example:
WAN Interface (wan, igb0)
LAN Interface (lan, igb1.223)
MGMT Interface (opt1, igb1.999)
All three elements must match (WAN, wan, igb0) (MGMT, opt1, igb1.999) in the same order.