"This is a serial number for a product that has been replaced" on AirPods Pro

My friend bought me the airpods pro and they were not working correctly and were malfunctioning a lot. When I enter the serial number into Apple's website to check its coverage, it says "We’re sorry, but this is a serial number for a product that has been replaced. Please check your information and re-enter your serial number. If your information is correct, you may need to contact us." As I understand these Airpods could be fake, my friend said they were bought from Best Buy so I doubt they are fake. What is the problem?

​[Re-Titled by Moderator]