Just an update on this, since I believe I’ve figured it out.
Mistake on my part, although it wasn’t all that clear.
To reiterate, the API was providing no response on user creation. So not even a failure response in the JSON, there was just no JSON.
The only thing that popped up was a 500 in the web server logs.
The API was providing a response for other actions such as getting all of the users, or getting a single user.
The problem seems to be that the API key/API username I was using was linked to a local account.
Local account auth was disabled due to the fact that we only use LDAP auth.
Enabling local account auth caused the API to respond properly to the user creation calls.
I’ll update this with some more information once I have access to the machine.
Should be fairly easy to reproduce, now.