serial number unavailable

You may be entering a character incorrectly, for example, mistaking a 0 for an O or an l for a 1. You will find your computer's serial number in About This Mac from the Apple menu. The serial number may be copied and pasted. If you are doing this already, then call Apple Support about the problem.

Contacting Apple Customer and Support Service

1. Apple Store Customer Service at 1-800-676-2775 or visit online Help for more information.
2. Primary support help at Contact Support.
3. To contact product and tech support:  Contacting Apple for support and service including international calling numbers.

Start with Check Your Service and Support Coverage - Apple Support.

If you're having trouble with that site, Contact Support and click through all the options until you have an opportunity to initiate a phone call or chat session.

Read this carefully. Realize your serial number may contain a zero but will not contain a letter "O".

Find the serial number of your Apple product - Apple Support

You need to purchase AppleCare within 60 days.

https://www.apple.com/support/products/mac/