Is there a difference between sandbox and prod key?

In most cases, your SEON Admin has two parts, the Production and Sandbox environments. These two are separate databases with different rulesets. 

The first is used mainly for the actual live feed of transactions, usually after the trial period ends. The latter, the Sandbox environment is used for testing the system, your integration, etc.

In order to send API requests to either one of these, you will need your license_key. To send transactions to the Production environment, you will need the Production license key, same goes for the Sandbox.