Trigger based on a VIP entering a building

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Hi, I'm new to scripting so I apologise if this is an easy answer.

I'm trying to make a trigger that if a U.N Officer (named "officer" in script) gets to a safehouse (currently an ambient building) the mission is won for the PMC's hired to protect him. I've been trying to find a way to get the trigger to activate once he enters the trigger zone but to no avail. If the safehouse must be changed to an empty unit building that is fine.

Any assistance would be appreciated.