To find your Close CRM API key, you need to click on your name in the bottom left corner and choose Settings.
Then, you will see a menu on the left, where you click on Your API Keys.
On the page layout, you will see a button New API Key
Click on it, enter API Key Name and press the Create API key button.
Notice. The generated API will be visible once only. So, do not forget to copy it before closing the window.