If you have a "mirrored" switch come in with your Portabee, the z-endstop can be very tricky. This is a modified z-endstop holder which can solve the problem. Note that a longer screw is required to tighten it properly.Print with just brim for adhesion support, should print without trouble. Put your mirrored z-endstop switch facing with electronics inwards (towards the printbet), the extra width of this holder will allow that.