PUT pre process script not triggered - modify payload

Hi I have this table in mysql database

messageID Int (Autoincrement)
Time varchar
Gas varchar
Temperature varchar
Humidity varchar
Pressure varchar

If I make a put request to may database with dreamfactory rest API I’m able to correctly insert into my database all the new data:

curl -d ‘{“resource”: [{“Time”:“2018-12-21T07:49:23”,“Gas”:“22”,“Pressure”:“222”,“Temperature”:“333”}]}’ -H “Content-Type: application/json” -X POST http://api.folin.org/api/v2/sensor_sql/_table/t?api_key=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Now if I want to modify data before insert them into database I use the following php scritp that is triggered my_sql_database._table.t.put.pre_process

<?php $payload = $event['request']['payload']; $url = 'sensor_sql/_table/t'; $api = $platform['api']; $post = $api->post; $myJSON = '{"resource": [{"Time":"1111-11-11T07:49:23","Gas":"1111","Pressure":"11111","Temperature":"1111"}]}'; $content = json_decode($myJSON,true); $result = $post($url,$content); var_dump($result); ?>

but it seems that it’s not triggered.
Now if I make a put request like before my data will be correctly inserted into my database but they aren’t modify buy the script rules.
How can I log my error ? Can you help me ?