There are two differences between the OpenShift documentation and the DMTF Redfish specification:
 
(1) Using PATCH instead of POST
--> OpenShift Container Platform 4.16 documentation Chapter has a list of required Redfish APIs [1], including usage examples. The API to "Check the ability to mount virtual media" requires the action "PATCH". However, the DMTF VirtualMedia schema [2] specifies the action "POST". Further the DMTF Redfish tacklebox [3] uses "POST" as well.
 
(2) Missing ETAG request header for PATCH operations
--> According to the Redfish specification the header field (-H "If-Match: <ETAG>") is required for PATCH operation. Most of the Redfish curl examples do not include this field.
 
[1] https://docs.redhat.com/en/documentation/openshift_container_platform/4.16/html/installing/deploying-installer-provisioned-clusters-on-bare-metal#verifying-support-for-redfish-apis_ipi-install-installation-workflow
 
[2] https://redfish.dmtf.org/schemas/v1/VirtualMedia.v1_6_4.json
 
[3] https://github.com/DMTF/Redfish-Tacklebox/tree/main/scripts