Login to your Zendesk account. In the right-hand corner of the page there is an icon of four squares click on this. 
This will produce a drop-down menu. Click on the Admin Centre at the bottom of the dropdown menu.
This will take you to the admin centre. On the left-hand side, there is a menu, click on Apps and Integrations to open the drop-down menu.
Click on Zendesk API under APIs.
Check “I agree to the Zendesk Terms of Service and Application Developer and API Licence Agreement and acknowledge that such terms govern my use of the Zendesk API” Box. This will only appear if you have never created an API token in Zendesk before.
Then click Get Started.
On the Zendesk API page, go to settings in the horizontal menu at the top of the page.
This will bring up the token access settings, enable both the Password access and Token access settings.
And click on the Add API token button.
Give the API token a name and copy the API token, by clicking on copy. Save it for later.