Please enter valid serial number
I am trying to find exchange value for iPhone 8Plus, but when I enter serial number it says "Please enter valid serial Number". I have no issue with anywhere else e.g. App store, subscriptions etc. My phone is almost 3 yrs old so when I put the serial no. in checkcoverage.apple.com, there too it says it is not valid (but may be because its outside warranty?). What should be my next step.
iPhone 8 Plus, iOS 14