Do not try to install octane if you are using octane with unity just go in free trail and select both agreement and it will help to get license of octane in unity.

Go to shop and accept all agreement and restart your unity you are good to go

In OTOY home page go to free trial tick book agreement than you open unity than download octane and in account use octane and in license use octane prime.

In OTOY home Page go to free trail and tick both agreement first tick on the pdf and second tick is below the pdf than your license will activate than open unity download octane than use octane in account and use Octane prime in license.