try this (note that this example fully overwrites the payload, you may want to add this to the additional payload instead)
POST _xpack/watcher/watch/_execute
{
"watch": {
"trigger": {
"schedule": {
"interval": "10s"
}
},
"input": {
"simple": {}
},
"actions": {
"log_error": {
"transform": {
"script": """
return [ 'date': Instant.ofEpochMilli(ctx.trigger.triggered_time.getMillis()).atZone(ZoneId.of("Europe/Copenhagen")) ]"""
},
"logging": {
"text": "Triggered time (UTC):{{ctx.trigger.triggered_time}} - Triggered time (Europe/Copenhagen): {{ctx.payload.date}}"
}
}
}
}
}