Hi Jonfurniss,
A 502 can be tricky since it could be caused by a variety of things. Have you taken a look at this post on the community forum, seems like someone else has run into this issue as well. Another installation guide you can confirm with is this one.
One other possibility could be maybe one of the application pools isn't started in IIS and that's why the OAuth server is not being accessed. You can check this by opening IIS and clicking on Application Pools on the left sidebar, then checking if the Aras OAuth AppPool ASP.NET Core is started. If you select that Application Pool you can confirm that the instance was installed/setup here as well by clicking "view applications" on the right sidebar.
Hope this helps!
Best,
Nithin
