Log error: {"code":"access_denied","message":"You are not authorized to perform this action."}

I recently added a feature to our company application to allow users to create fresh service tickets through a web page. I use my API key in the request and when testing I was testing as myself and creating tickets locally on my development environment and they were successfully appearing in our fresh service inbox. On production I used the same api key for the following endpoint  /api/v2/tickets and I get the following error.
Log error: {"code":"access_denied","message":"You are not authorized to perform this action."} it also logs the same error when other users are trying to create a ticket.

Just wondering if there is a feature that can be turned on to make this work. OR If I need to be using a different API key or a different plan to allow other users to create tickets from within our application.