$util.validate($util.matches("^[0-9a-f]{8}-(?:[0-9a-f]{4}-){3}[0-9a-f]{12}$", $ctx.args.sourceId), "Invalid ID")

#foreach( $instance in $ctx.args.instanceIdSet )
    #set($instance = $util.urlDecode($instance))    
#end

{"version": "2017-02-28", "operation": "Invoke", "payload": $util.toJson($ctx)}