How to edit custom properties when importing Bitrix?

Question

1C-Bitrix

To be honest, I already cursed the day when I agreed to help my friends with the site on Bitrix. I googled and searched for a long time in the documentation, but did not find a solution to the obvious question:
I hang the AddEventHandler("iblock", "OnBeforeIBlockElementAdd", "test"); when importing csv

function test(&$arFields) {
header('Content-Type: application/json');
echo (json_encode($arFields)); exit;
}

Gives me the standard infoblock properties, how can I perform operations with custom ones that I added myself?
(I'm attaching the json output)

And the second question, how can I even operate with the request / post data?

Answer 1

Well, for starters, at least open the documentation https://dev.1c-bitrix.ru/api_help/iblock/events/on... and see how it's done in examples