Print Webhook API payload in PHP

I am sending over the below payload from Postman to a PHP endpoint using a POST:

{
  "email": "myemail@yahoo.com",
  "overwrite": true,
  "fields": {
    "first_name": "John Doe",
    "country": "Chile",
    "mrc_c3": "25.00",
    "mrc_date_c3": "10/10/24"
  }
}

Over in the PHP script, I have the below code:

<?php
  require_once("db.php");

  $payload = json_decode(file_get_contents("php://input"), true)["payload"];

  echo "this is the payload: " . $payload[];
?>

As you see in the above, I attempted to just echo out the payload array, but Postman is only printing out "this is the payload" and nothing else.

How can I edit the above code so that it displays the payload that I sent from Postman?

I see two problems:

First, you're referencing an array key named payload but you don't have any key named that:

$payload = json_decode(file_get_contents("php://input"), true)["payload"];
                                                                ^^^^^^^

You probably just want to decode the body as a whole:

$payload = json_decode(file_get_contents("php://input"), true);

Then you'll get:

echo $payload['email']; // myemail@yahoo.com
echo $payload['fields']['country']; // Chile

Second, using the array braces here is a syntax error:

echo "this is the payload: " . $payload[];
                                       ^^

If you want to refer to the whole array, just use $payload by itself. However, note that you can't just echo an array, as echo is for scalar values only. You could do:

$payload = json_decode(file_get_contents("php://input"), true);
print_r($payload);

And you'll get:

Array
(
    [email] => myemail@yahoo.com
    [overwrite] => 1
    [fields] => Array
        (
            [first_name] => John Doe
            [country] => Chile
            [mrc_c3] => 25.00
            [mrc_date_c3] => 10/10/24
        )

)