Lost activation key from 2016

Hello, I purchased an R8 recorder in 2016. Included with the R8 was an activation key to access steinbergs CUBASE. I downloaded CUBEBASE with the activation key. I have not used cubase since 2016. I opened cubase yesterday and it is asking for the activation key. I no long have the key as the paper has been lost. Do you have any suggestions as to how or if i can access the key and or cubase to use with my R8?
Any suggestions or advice will be appreciated.

Thank you

If you activated the license, the paper is no longer good anyway. You may need to reactivate the license. Did you REGISTER the license in your My Steinberg account? If so, reactivation should be easy but if not, it may be a loss.