getParam retrieving null instead of user data - php

Question

I'm trying to post new user signup to the data using getParam, I used RestClient to test if value is retrieved or not turns out to be null every time:
this is the json data I put in the body, and I do add a content type header based on application/json:
{
"email" : "test#test.com",
"username" : "test",
"password" : "123",
}
This is the code for posting user (note that var_dump($email) and die I used it just to check $email does contain a value or not, will be removed when it is fixed):
//add new user
$app->post('/user/add', function(Request $request, Response $response){
$email = $request->getParam('email');
$username = $request->getParam('username');
$password = $request->getParam('password');
$sql = "INSERT INTO users (email, username, password) VALUES (?, ?, ?)";
var_dump($email);
die ("end");
$conn = new Database();
$conn = $conn->createConnection();
$stmt = $conn->prepare($sql);
$stmt->bind_param('sss', $email, $username, $password);
$check = $stmt->execute();
$error = $stmt->error;
if ($check){
echo 'Added Successful';
}
if ($error != ''){
echo $error;
}
});
I did the same thing for posting appoinment by /calendar/add and it work prefectly, bot post method are the same but why post user is not getting the value?

Answer 1

getParam() is only used for query parameters like: yoururl.com?param1=value1
You have to use
$body = $request->getParsedBody();
echo $body['email'];
instead

Answer 2

DZDomi's answer is not quite accurate because getParam() of Request class does call getParsedBody() method internally. It should work with query strings or data from POST body.
If you get NULL when sending POST request, make sure that you setup client to use application/x-www-form-urlencoded or multipart/form-data.
I do not know about RestClient, but if you use Postman, you can define this information on Body tab on Postman UI.