Apple Watch series 5 serial number

I ordered an apple watch series 5 from amazon a little under 2 months and tonight while on the apple website trying to get service it asked that i gave the watches serial number. After typing it in, apple keeps saying that it is an invalid serial number. The watch is registered to my apple ID so i see the option to click on it but everytime it says invalid serial number. I was wondering what to do about this.