In order to retrieve and push your data in a secure manner, two mandatory parameters are to be used while using APIs.
Every account will carry a general authtoken for the account's API access. Follow the below steps to retrieve your authtoken.

To access list management API methods, in addition to your authentication parameters, a mandatory parameter "listkey" is to be used. The listkey represents the mailing list you're trying to access.

Note:
In any given scenario, be it any kind of API, we advice you to follow what is given in this document. keys are sensitive and any kind of typo during request could result in an error case. However, we thought we should let you know of some points to keep in mind:
For further assistance, please contact us at support@zohocampaigns.com