Users can be updated via API using the "Create or update multiple users at once" request. The value for the field "username" and "external_id" must also be sent. The "username" and the "external_id" of existing users can be found out via the "Get all existing users" request.
Info: Users created in the app or via the Excel import do not have an external_id. In order to be able to synchronise them via API, the user name ("username") must be sent in the "Create or update multiple users at once" request for a user. The user must also be given an "external_id".