How to get HA to speak a sentence from an Automations Webhook trigger

I am using Whisper, Piper, Wakeword and Assist Mic with HAOS on Pi4.

I can set up an automation to trigger from ‘sentence’ then do ‘set conversation response’ to make HA verbally reply to my sentence.

What I want to do is have HA verbally reply when a Webhook is triggered.

I have successfully set up a webhook which turns my TV on and OFF, however
if I add action and select ‘set conversation response’ to make HA verbally respond, it doesn’t. I presume this is because conversation response only triggers when the automation was triggered by conversation trigger. My question is, how do I get HA to verbally respond following a webhook trigger.

In summary:-

Webhook triggered, HA responds verbally with a fixed sentence.

Many Thanks

Colin