Problem: PopClip's copy and paste, spelling replacement etc. are not working immediately after updating to Mojave.
Solution: The following steps should resolve the problem. If not, please get in touch.
1. Quit PopClip
2. Go to System Preferences → Privacy → Acccessibility
3. In the list "Allow the apps below to control your computer", highlight PopClip and then remove it using the "-" (minus) button.
4. Use the "+" button add PopClip again to the "Allow the apps below to control your computer" list.