Always getting "We’re sorry, but this serial number isn’t valid. Please check your information and try again." when generating serial number.

I am trying to generate a serial number, but from what I read, if I am getting the "We’re sorry, but this serial number isn’t valid. Please check your information and try again." that means I need to keep generating one till I get the message, "We're sorry, the number you have provided cannot be found in our records. Please verify the number and try again"

I must have now tried 30 times. What is the secret on generating one that will give me the message, "We're sorry, the number you have provided cannot be found in our records. Please verify the number and try again"??

Author: @mbze430