Try rel path

schemas/data-ingress/pushport/ts.json

@@ -33,7 +33,7 @@
         "locations": {
             "type": "array",
             "description": "A list of one or more locations where the train has recorded a movement or forecast",
-            "items": { "$ref": "pushport/ts_location.json" }
+            "items": { "$ref": "./ts_location.json" }
         }
     }
 }