Nick ,
Many thanks for the reply & pointing out the location of the reference. For others I can confirm that the following works with my payload formatter as per my original post.
curl --location \
--header 'Authorization: Bearer NNSXS.<your downlink api key>' \
--header 'Content-Type: application/json' \
--header 'User-Agent: my-integration/my-integration-version' \
--request POST \
--data '{
"downlinks": [{
"decoded_payload": {"data": {"state1":"false"}},
"f_port": 1,
"priority":"NORMAL"
}]
}' \
'https://eu1.cloud.thethings.network/api/v3/as/applications/heltec-esp32-otaa-led1/webhooks/testhook2/devices/22......9909/down/push'
Regards,