Unauthorized Error: Creating tokens

Hi all,

We are trying to use Zendesk API to get tokens to be used to create tickets via Workday Studio integration. 

We have created a new Admin User in Zendesk and trying to use the credentials to make the call. When I try to use Admin credentials I get the error: Error Authenticating the Zendesk API: Unauthorized

The Authentication URL we are using is of the format as shown below:

https://<xxxxx>.zendesk.com/api/v2/oauth/tokens.json

I am able to login correctly via front end for the same user though.
Can you please let me know what are we missing?