I’ve created my first simple plugin and compiled it in AU and VST3. It works fine on my mac (macOs Mojave 10.14.6) and on my Ableton (10.1.3).
I tried to send my .component and .vst3 to some friends to test the plugin, but they had problems when they tried to open it in Ableton (same version of Ableton and macOs). The plugin is shown inside the Daw, but, when they drag it, an error appears. I really don’t understand what could be the problem.
Moreover I tried to send my .vst3 also to friends with Windows, but in this case the plugin does not appear in the vst3 list inside the DAW (also after doing the rescan of plugins).
So you sent the VST3 compiled on Mac OS to your friends using Windows? If that is the case, that won’t work, you need to compile a separate windows version of your plugin on a Windows machine.
“error appears” is not really specific. What kind of errors are they experiencing? A crash? If so, then you should have a look at the call stack contained in the crash log that MacOS usually generates in such cases, this will most likely give you a hint in which function call your plugin crashed. If you sent them a debug build instead of a release build, this output will even be quite more verbose.
Do you by chance dynamically link against some library that could not exist on your friends’ systems?