Hi, Guilherme.
If you would like a suggestion: building up from simple to more complex usually helps a lot with learning new things. We have pretty good docs on SCIM, like [here](https://gluu.org/docs/gluu-server/4.2/user-management/scim2/#creating-resources) it shows a simple JSON you can use to create an user. It works, I used it several times, so you could start from here, and then add the attributes you need one by one, testing user creation after each of them - until you'll find out which of them give you the trouble, or find what you were doing wrong perhaps.
Hope this helps, feel free to create another ticket if you'll be stuck at some point again.