Warning: Before I write anything, if you're going to try the same, it's a request not to use this "@opsgenie.com" domain to create a user. There's a serious issue with your "@opsgenie.com" domain and other domain.
Let's explain you the scenario:
1. I'm trying to create a user, using postman

2. After "created" response, I have tried to do a get by user id, and surprisingly the "fullName" is mismatched. If you notice it property the "fullName" is nothing but the first part of your "username".

3. Here's the UI result
