Atlas currently only allows that 100 MongoDB users be created per group. It may be worth updating Add MongoDB Users and/or Create a Database User sections of the Atlas documentation to mention this limit.

If a user attempts to exceed this limit via the Atlas API, the following response is returned:

{ detail: 'Groups can contain at most 100 database users.', error: 403, errorCode: 'GROUP_USERS_LIMIT_EXCEEDED', parameters: [ 100 ], reason: 'Forbidden' }