External sliding door handle: what is this dark magic?

[qqwertyy]

Hi all, will try to keep it short and sweet for you nice folks!

Had to replace external sliding door handle on 2009 Transit Connect. Got the old one out, slotted the new one in.

However, it's just hanging out of the slots that the old one sat in, clearly hasn't latched onto whatever mechanism is needed to actually lock and unlock door:

TC handle 4.jpg

From the inside of the van, I've removed the inner door handle (which is the only way you can access the screws for the external handle anyway), and taken a photo of what looks like the locking mechanism).

TC handle 2.jpg

TC handle 3.jpg

I think what's happening is that the hook on the handle, circled in the pic below, needs to fit behind the little metal triangle circled in the pics above. Then when the handle is pulled it tugs on that little triangle and unlocks the door.

TC handle 1.png

However:
a) it seems impossible to slide the handle in and get that hook BEHIND the mechanism
b) The metal bit is too stiff and too thin, I can't manage to get a screwdriver or anything on it to push from the other side and test it out.

Anyone changed one of these who can advise?

Cheers!!!