Hi @conor.mccarthy
Thanks for reaching out to the Zoom Developer Forum and welcome to our community!
Can you please confirm if you are getting the token with the appropriate scopes to access the Get Users endpoint?
If you are calling the Get users endpoint, make sure that your Server to Server OAuth apps, has the scope user:read:admin enabled.
Here is a post that I created a couple of months ago on how to use our Server to Server OAuth app with Postman:
Let me know if this helps,
Elisa