In the swagger documentation for the /workgroups/users API (https://app.swaggerhub.com/apis-docs/magicplan/magicplanCloudApi/1.2#/), the response is specified as having a "data" property which is an array of objects.
In fact, the "data" property is an object that contains paging information, and a "users" key which is an array.
It would be useful to update the documentation to account for this, and include paging/filtering API parameters, since none are mentioned.