When PAM Admin attempt to delete a Proxy Agent out of PAM, the get the following error:
Error: PAM-UI-2203: Error deleting proxy. Proxy cannot be deleted because it is in use.
Release : 3.4.x and 4.0.x
Component : Privileged Access Management
Go into the PAM UI >> Credentials >> Managed Targets >> Applications.
Here do a filter on "Application Type" = "Windows Proxy"
Then on all of the applications that come back, go into them and look at the "Windows Proxy" Tab and see if that server is being used in the selected Proxy section.