Duplicate Cleaner 4 won’t run on Windows XP. Version 4 requires the Microsoft .NET Framework 4.5 which isn’t supported on Windows XP.
However, Duplicate Cleaner version 3 does run on XP. If you have a version 4 license but would like to run version 3 on Windows XP, then drop them a support ticket and they’ll issue a version 3 license you can use.