Follow the instrustions to the letter. It works 99.999% of the time.
If you STILL see the flashbridge error. Open your Activity Monitor (it's in the Mac HD/Applications/Utilities folder). Look for "activmgr" and stop the process. Otherwise, in the Menu Bar along the top of the Mac desktop: it is a tiny red "X." If you pull down the icon, there is an option that will let you quit the "flashbridge-wrapper-crossplatform."
Search for Activity Monitor
Find flashbridge-wrapper-crossplatform and highlight it
Click the Stop button on the top left