Incorrect Serial number

The serial number is also somewhere on the surface of your Mac, depending on model. See this support topic:

https://support.apple.com/en-us/HT204308

The serial number may be different than what is reported in About this Mac, if the motherboard was replaced.

First see if it matches the serial number on the machine. On a laptop it would be engraved on the bottom. On an iMac it would be on the bottom of the stand. If they don't match, type in the one on the machine