Yes, I had the answer from Meraki about this but there is so much problems with Meraki Auth Users, I don't think we'll be able to use it.
When we create a user from the web portal, the ID format is not the same as when we create it from the API.
Ex:
From Web portal: YWMtcGYyYm6xM3NAdnBuLmFkZGNhcCxDbGllbnQgVlBO
From API: ZmFrZUBlbWFpbC5jb10sQ2xpZW50IFZQTg==
When created from the web portal, I can Update and delete the user from the API.
When created from the API, I can't update or delete it as the ID format is not good.
The "Delete" fonction doesn't remove the user but disable the vpn connection capability and still remain in the list from the webportal, but I can't reach it from the API.
Looks like different people was working on different parts of the code without talking to each other.