I use the adaptor on my B96 with a SodaStream, are you missing a part to mate it to the pistol? That looks like an aftermarket foam set up there, maybe you didnt get all the bits. I cannot actually remember if mine came with one, perhaps I got it as an aftermarket as well.. I know the one I got could be used on an XS78 chinese rifle as well, maybe from Archer Airguns?

Anyway, there is a fitting and you can make it work with SodaStream if you want.