Hi!
Sorry for the delay I just came back from vacation.
In general BetterSnapTool works fine on Mojave, however Mojave is still buggy in some areas (which I have reported to Apple). Please try to follow the tips posted here: BTT doesnt start in macOS 10.14 Mojave they should also work for BST.
However one note: beta software is always buggy. You shouldn't install it on your main working machine and you should definitely not expect every paid app working on a beta version of an operating system. There are many things we developers can not influence.