Why, despite installing the license, is Merlin Project 4 still in demo mode?
Please check the Merlin Project license window (Merlin Project/Preferences) to ensure the license has been installed correctly.
One possibility is that you may have started Merlin multiple times. Please ensure that you only start as many instances of Merlin Project as you have licenses for. Once you close the additional instances, the license will be released again and you can continue working with the licensed version.
Another possibility is that your license might be an upgrade license. An upgrade license is only valid together with the previous license(s). So if not all your previous licenses (Merlin 2, Merlin 1) are yet installed you should correct this to have your Merlin Project licensed correctly.