On the Swap Exchanges page you can see how many API slots your license has, and enter up to this number of API keys to be registered for use.
To register a new key, follow these steps:
Make sure the Gunbot core is running, without errors, on an already registered API key
Go to the Swap Exchanges page, select the exchange, enter your key and save the changes.
Refresh the page in case you don't see the form to update your keys.
After registering a key, you can use it as Master Key in your exchange settings.
You can also use the Swap Exchanges page to update an already registered key for one of your exchange accounts. Just use the steps described above and overwrite the old key.