Where is the APM/SWG Assign URL Filter action?

Where is the APM/SWG Assign URL Filter action within the VPE for per-request policies? I have a URL filter defined, but all the manual says is "To put a URL filter into effect, you must assign it in a per-request policy. A per-request policy runs each time a URL request is made." I may be blind, but I'm not seeing URL Filter under the Assignments tab (or any other) when editing the per-request policy. (v12.1.1).