Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Office Professional Plus 2016 is normally a volume license, intended for large corporations. The only exception was if you were able to purchase it via the HUP (Home Use Program); in that case, see https://www.microsoft.com/en-us/workplace-discount-program/order-history .
If you purchased this version from a third-party reseller, you have been scammed, I'm afraid. The license may work for a while, sometimes even for years, but at some point Microsoft will revoke the product key because of invalid use. You didn't do anything wrong; you were scammed, but the end result is that you have now lost the Office product of course.