G-Lynx ATAS (AIM-92) won't lock onto target

Although I realise that I might be doing something wrong (most likely), I can’t get the G-Lynx to lock and fire ATAS (Stinger) missiles in the test-flight scenario. (In SIM mode.)
I can select the weapon, and I get the thing to start beeping too… but it won’t lock onto the target, even though I have the target selected.

Are there some keybinds I need to consider to get this to work?
Am I doing something wrong?

Are you within the lock range for the weapon? It can’t lock on at any range, it has to be within 6km.

Yes I am. I read up on min and max ranges for engaging with this weapon.
As far as I can tell, everything is as it should be. Aspect… Range… Direction… tea hot… everything.

Make a test flight in external view and look at locking circle when you press the “lock” button. IIRC manpad mounts aren’t vertically aligned with its carrier (your helicopter). So you might have to go nose-down from your target to be able to lock it.