Congrats on getting the new equipment. I beg you to pray for the keymakers. A common door lock is a much more complicated device. Even if both locks were new, could it not be more likely that one of the locks does not work as well as the other? I would think that the key for the lock that doesn't work was made by the exact same process as the one to the working lock.
Did the keymaker not reproduce the master four times? By dong that and arguing with you he has probably consumed all profit, therefore he has enough trouble.
Sometimes the repro keys have an unclean cut, like a rough not smooth edge. It is usual to round down all the edges of the key. Advisable too is the use of additional lubricant
Following that if it still doesn't work, I would be as worried with the small cost of the key but whether or not the lock is defective.
I once put in a lock as it was touted to be a super-protective new style. Once I had come home to take lunch and had a limited amount of time to get back to work. I turned the lock and pulled out the key and the entire lock cylinder came out of its housing!
Like I said I did not have the time and wanted the door locked. So I just put the thing back in place and tried it and it locked and didn't come out a second time. Every time after that, I actually kept trying to pull the lock out with the key and it never happened again. I knew the lock had a defect, but never could replicate the cylinder coming out.
So locks can be tricky. See if you cannot get the lock exchanged, and make sure you do not put it in upside down.