When downloading Duplicate Cleaner Pro from our website or elsewhere, The Microsoft Store may recommend you install the version from its own Store (free, not Pro).  You may get a screen looking like the below:

In this case, don't click the 'Install' button, instead click 'Continue installing from outside the Microsoft store' , as circled in red above.

If you don't even get this option, this setting in your Windows Control panel may help.  Go to Apps and Features, and change "Choose Where to Get Apps" to "Anywhere".  You may need to restart your PC afterwards.