I looked up serial number in About This Mac and Support site says it isn't

Question

I can't find my Apple Care plan or read the bottom of the computer but I looked up the serial number on my iMac under About This Mac. I copied and pasted it into the box to get a call for technical support and I get a message saying it is not the right number. Now what? How can I call them to get support without the number?

Answer 1

A valid Apple product serial number is eleven characters long, does not contain the letters I or O—though the numerals 1 and 0 are valid characters—contains the numeral 0 though 9 in the third position and the numeric string 01 through 52 in the fourth and fifth positions.
On your model, it's found screened beneath a barcode on the underside of your foot, or can be found as you were instructed using About This Mac or using the System Profiler application. If your logic board has been replaced and is not the original unit installed at the time of manufacture, your logic board may not have the serial number embedded in firmware. In that case, it is not available to display using the About This Mac dialog or the System Profile application.
The most reliable source of such information is typically the number screened on, inscribed or affixed by label to your Apple product.