Answer
Double-check that the Bound Entity Set Name and Bound Entity Set Parameters document properties on the connector aren't swapped — the entity set name is the fixed set name from the URL (like the resource's own Set name), while the bound parameter is the actual dynamic value (like the extracted ObjKey) that needs to vary per record; setting a Dynamic Process Property via a Set Property shape before the final connector step, then mapping that property into the Bound Entity Set Parameters field specifically (not the Set Name field), is the reliable way to wire this up.