While preparing the order i noticed that the website doesn't accept game packs (For an example try to request AquaNox + AquaNox 2) it gives back an error, possible unimplemention or thing done on purpose because only ids connected to games can be written on the request game page?
I'm not sure why that would happen, it seems to work for me:
https://steambitshop.com/?page=request&search=4237