You can find your API key in your shipcloud WebUI by clicking on your email address in the top right corner and then on "API Key".
There you will find two keys: your sandbox key and your API key. For testing purposes please use the sandbox key. To be able to generate live shipping labels, please use the live key.
Please note that you can only access both keys via the live environment. They are therefore not displayed in the sandbox or test environment.
For more information about live and sandbox mode, click here.