I would be suspicious of purchasing anything to install an Apple OS from Amazon. Why don’t you make your own USB stick so that you know what you are getting is an “official” release of macOS Mojave from Apple. There is no telling what is on that stick or how old the software is.
Here is Apple’s page for installing older versions of macOS:
How to create a bootable installer for macOS
Sorry I don’t have a better answer for you, but your next step might be to post on the official Apple forums and if you tell them you bought an USB stick with Mojave on Amazon, they are not going to support you.
If I remember correctly, the firmware on my 2010 Mac Pro needed to be updated before I could upgrade to Mojave. There were steps to update the firmware that needed to be followed before installing macOS. Maybe the 2012 Mac Pro doesn’t need this? But that is something to look into.