Have you updated Nimble Kick to 1.0.2 yet?
Also, try this: go to "System Preferences > Security and Privacy > General" immediately after you get that error, you might see a button there to allow Nimble Kick to run.
(In any case, even though it should work in most situations, I'm going to make sure it works 100% on MacOS 10.15 soon.. Apple made it quite a headache unfortunately.)