Eventide Staff
Since he has it in front of him, he is probably right. For the record, the ring is not connected to in the TF socket, so it does not care whether you use a TS or TRS. It is possible that the pedal expects the ring to be connected to something – I'm at this moment looking at a Line6 pedal, which also has the ring unconnected, but others may be different.
My suggestion is that you get your unit back from the dealer and buy the cable from him.