Troubleshooting Appwrite PHP Function: Document Deletion Issue

Question

I have implemented a PHP function in an Appwrite project with the goal of deleting a document. However, the function is not working as expected, and I need assistance in troubleshooting the issue. The function is designed to receive a document ID as input and use the Appwrite PHP SDK to delete the corresponding document from the specified collection. In the code below, after I send a payload with document ID and execute it, the response is: 'Missing required data: documentId'.

<?php

use Appwrite\Client;
use Appwrite\Services\Databases;

require_once 'vendor/autoload.php';

error_reporting(E_ALL);
ini_set('display_errors', '1');

return function ($req, $res) {
    $client = new Client();
    $database = new Databases($client);

    if (
        empty($req['variables']['APPWRITE_FUNCTION_ENDPOINT']) ||
        empty($req['variables']['APPWRITE_FUNCTION_API_KEY']) ||
        empty($req['variables']['APPWRITE_FUNCTION_PROJECT_ID'])
    ) {
        return $res->send('Environment variables are not set. Function cannot use Appwrite SDK.', 500);
    }

    $client
        ->setEndpoint($req['variables']['APPWRITE_FUNCTION_ENDPOINT'])
        ->setProject($req['variables']['APPWRITE_FUNCTION_PROJECT_ID'])
        ->setKey($req['variables']['APPWRITE_FUNCTION_API_KEY'])
        ->setSelfSigned(true);

    try {
        $data = json_decode($req['payload'], true);
    } catch (\Exception $err) {
        $res->json([
            'success' => false,
            'message' => 'Payload is invalid.',
        ]);
        return;
    }

    $documentId = $data['documentId'] ?? '';
    $databaseId = 'conni';
    $collectionId = 'innocaps';

    if (empty($documentId)) {
        return $res->send('Missing required data: documentId', 400);
    }

    try {
        $response = $database->deleteDocument($databaseId, $collectionId, [$documentId]);
    } catch (AppwriteException $error) {
        echo $error->getMessage();
        return;
    }

    $response = [
        'documentId' => $documentId
    ];

    return $res->json(['user' => $user]);
};