Hi @tiago.diogo,
Check the headers of your response when you create the user. It should contain the location of the newly created user. You can get the id by cutting it of that String.
A header ‘Location’ should be present in the response and should look like http://localhost:8088/auth/admin/realms/realm-name/users/12f2e22b-8137-495f-bccc-50bb15cdf0ec