You can find the answers to many questions here, it’s very likely someone before experienced the same problem as you do. Otherwise you can also submit an issue ticket and wait for our help.
Basically the demo version and full version of a d16 plug-in are same binary file. That allows you, after a purchase, to activate the plug-in (working as demo) to a fully activated one. Don't be supriprised when you see plug-in asking for a key file (black splash window) even if you install the demo; you may ignore it, and click somewhere on GUI outside the black box to continue evaluating demo version and close the popup black window.
Note that black splash window in a demo version, apart from link to the shop and button allowing plug-in activation, contains also some useful information like demo limitations.
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