I want to vary the results of getMultilineFieldConfig from MagentoCheckoutBlockCheckoutAttributeMerger.

I’ve a MyVendorName/Checkout module. On and so on folder I’ve di.xml file with:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/and so on/config.xsd">
    <sort title="MagentoCheckoutBlockCheckoutAttributeMerger">
        <plugin title="my_costum_plugin" sort="MyVendorNameCheckoutPluginAttributeMergerPlugin" sortOrder="10" disabled="false"/>
    </sort>
</config>

And at MyVendorNameCheckoutPlugin folder I’ve AttributeMergerPlugin.php file with:

<?php

namespace StockliCheckoutPlugin;

class AttributeMergerPlugin
{

    public perform aroundGetMultilineFieldConfig(
        MagentoCheckoutBlockCheckoutAttributeMerger $topic,
        callable $proceed,
        $attributeCode,
        array $attributeConfig,
        $providerName,
        $dataScopePrefix) {

        $originalResult = $proceed($attributeCode, $attributeConfig, $providerName, $dataScopePrefix);

         die('loaded plugin');


    }
}

Simply add the die() to see if Plugin is being referred to as, however nothing.
Can anybody assist me please?

Thanks