Rekordbox Record Function & License Key Number

Hi,

I recently bought a new MacBook Pro and have installed a fresh new version of Rekordbx onto it. I'm now ready to record some new mixes but it is asking me to - 'activate my license key to perform on the connected equipment' (I connected my laptop to a USB cable that links to my mixer. I read that you can find your license key on a piece of paper that came with the CDJ's? Only thing is I bought my CDJ 2000 NXS and DJM 900 NXS second hand. How can I find my license number so I can start recording? Do I need my license key number to record?

Please get back to me as soon as possible. 

Thank you,

Ayla Thomas.