Typically, this issue is caused by a space entered either before or after the key. Ensure that there are no spaces either at the beginning or end of the key you have inserted.
If Camtasia for Mac was working with your key, and is suddenly asking for your key but will not accept it, please first ensure that you are licensed for the version you have installed. If you have the correct version installed, please exit Camtasia and delete the following files if they exist:
- /Users/<your username>/Library/Preferences/com.techsmith.camtasia.plist
- /Users/<your username>/Library/Preferences/Camtasia Registration Key
- /Users/Shared/TechSmith/Camtasia/Camtasia Registration Key
Then, re-open Camtasia and attempt to input the key again.