Difference between users and contacts in API
While reading the API documentations I came through two API's one is list contact and another is list user
what is the actual difference between them. Whether I need to add my assignee to contacts or users using API.
Contacts and Users are two different types of Smartsheet accounts that you can retrieve.
List Users will gets a list of users in the organization account. https://smartsheet.redoc.ly/#operation/list-users
For example, if you are on a Business account with 3 licensed users and 2 unlicensed members, this would identify all 5 of those accounts. Here's the documentation on the different types of users you can add to an organization: Account-Level User Types
However, List Contacts is specific to your personal login and who you have added to "My Contacts". https://smartsheet.redoc.ly/#operation/list-contacts
This will include Contacts you have added, such as a client who has a Pro account, or a Free User that does not belong to any organization, or a friend who has a license on an Enterprise account. See: Manage contacts in the My Smartsheet Contacts list