I’m not entirely sure why this has happened. Normally you can run the installation again and it will work. If you continue to have trouble, make sure you look at the steps in https://help.keyman.com/products/mac/current-version/start/install-keyman and pay particular attention to the information about required permissions for Keyman to run.
Thanks Mark. The link you provided must have a more recent installer as I downloaded that and it installed successfully. Many thanks for getting back to us. Cheers