See the instructions in this video
Additional steps for a newer macOS:
Open System Preferences > Security & Privacy > Privacy tab
Unlock the padlock at the lower-left with an admin username and password
Click on Input Monitoring
Open a Finder window and locate the file shown below
Drag-and-drop that file into the right side of the Privacy tab if it's not already there and make sure its box is checked
Then click on Accessibility and drag-and-drop the same file into that section and make sure its box is checked