Tricky zipper installation!

Sergio, from Spain. This is the first time I write here, bear with me for my english... I may get some words wrong 😅

I am making a bifold wallet for my mum and she asked for a coin pocket with a zipper like this one on the pic below:

I understand the main idea of how it works, but I have no idea of how to install that zipper, since both pieces are different lenght and they move apart from each other when opening.

I have got this far with no issues:

Im using buttero leather with 0,8-1mm for the orange pieces and 1,6-1,8mm for the blue (no skiving service on that supplier). But i skived the "wing" to 0,6-0,7mm all around for a better folding.

Any tips?