Unity OS 5.3 uses xml format license keys only.  Older .lic keys will not work, so you need to make sure you're on 5.3 in order to apply the xml format license.
I have received evaluation license for UnityVSA in .xml format. But when I try to import it to my UnityVSA appliance shows "The file being selected must have a suffix of ".lic"." How can I convert my .xml license to .lic format?
How to convert UnityVSA Evaluation License from .xml to .lic format?