Sensetecnic FRED TTN Downlink

I have a Laird Lora Gateway linked to a TTN account which contains an application (marlborough) and a device (esp32).

I also have a FRED (NodeRed) account which has three TTN nodes configured - TTN Event, TTN Uplink and TTN Downlink.

The TTN Event and TTN Uplink function correctly i.e. I see messages transmitted from my end device appear on the FRED page.

I cannot get the TTN Downlink to work.

Has anyone had any success?

Thanks

Ian