Windchill REST Services endpoint to create a PartUsageLink is missing

Version: Windchill 12.1

Use Case: I am attempting to create a PartUsageLink using Windchill REST services: URL: POST /ProdMgmt/Parts('{PartId}')/Uses

Description:

A Vanilla build of Windchill allows me to create a PartUsageLink using this REST endpoint. However, when we deploy our Implementation Partner's CCD build to our environment, that endpoint is no longer available. They are not sure why this is. There are no customizations or configurations done to any REST endpoints directly. What would cause this problem and how can I make this endpoint available again?

Below is a pic showing the REST endpoint available in our DEV environment (Vanilla) vs. our INT environment (with configurations deployed).

When I attempt to hit the endpoint in INT I get this response:

{
 "error": {
 "code": "OPERATION_NOT_SUPPORTED",
 "message": "The operation is not supported"
 }
}

The POST /ProdMgmt/Parts('{PartId}')/PTC.ProdMgmt.CreateUses returns the same error. Thank you for any help or suggestions!