First of all.. I am a FPD newby.. but I felt OK working on Wordpress with it so far. Documentation is also quite good.

So I got it to run without complications. But here comes the "but". 

I offer Spice-Cans to my customers, as a Product Variant I want to offer the "Customization" of the label design. So I found FPD, installed, created FPD Product and added it to Product-Variant. 

Images show Backend and Frontend. 

It is my understanding after reading the Documentation, that once a FPD Variant is selected, the Customizer opens.. but.. and this is my issue: it doesn't.

When i create a simple Product and define it as a FDP Product - it works.  example:  (http://schmalys.com/produkt/lisas-fishers-love-2/)

Checking Debug-Status Template is working OK.

Can anyone help me or let me know if I am missing some steps? or is this another issue?

No, it does not open automatically once a variation is selected. You still have to have:

1) a product selected as initial product in the source field - so that FPD loads at all.

2) an appropriate position selected for FPD to open (settings, general tab and WooCommerce tab).