Second-hand UR28M license issue

With the exception of Rev-X, the other effects (Channel Strip, Amp sims) are hardware based (in the UR) and not offered as separate VST plugins. What you seem to be describing is re-amping if I understand you correctly, and this is possible, but through the hardware.
If your problem is in fact license based, then you’re probably best to open a support request in your “My Steinberg” account in this regard.