Fetch data from mysql and if the result === 0 then do something - php

Question

My main task is to create a contacts list. So the user presses the button, then the user sees on the screen, types in an Email of contact user and then if the response from server is "result === 0" the contact user will be successfully added to the contacts list. If the response from server is "result === -1", then the user was not found because of email does not exist.
Everything works fine, except one thing: even when the Email is wrong, it shows that the response from the user was successful.
I can't find what I do wrong. Can anyone help me please?
Here is my code:
Contact List (React Native):
addNewContact = (email) => {
this.setState({
promptVisible: false,
});
if (email === this.props.email) {
Alert.alert('This is your username', 'You cannot add yourself to contacts!');
return;
}
for (var i = 0; i < this.state.contacts.length; i++) {
if (email === this.state.contacts[i].email) {
Alert.alert('Existing Contact', 'Contact ' + email + ' already exists');
return;
}
}
this.showLoading();
fetch('LINK')
.then((response) => response.json())
.then((responseData) => {
this.hideLoading();
var result = responseData.result;
var contactId = responseData.id;
var name = responseData.name;
if (result === 0) {
console.log("Success");
var newContacts = this.state.contacts.slice();
newContacts[newContacts.length] = {
contact_id: contactId,
name: name,
email: email
}
this.setState({
dataSource: this.state.dataSource.cloneWithRows(newContacts),
contacts: newContacts
});
Alert.alert('Contact added', 'User ' + email + ' was added to your contacts')
console.log(newContacts);
} else {
if (result === -1) {
Alert.alert('Not Found', 'User ' + email + ' not found');
console.log("Bad");
console.log(responseData);
}
}
})
.done;
}
Server (PHP):
<?php
include 'DBConfig.php';
$conn = new mysqli($Name, $User, $Pass, $Database);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$json = file_get_contents('php://input');
$obj = json_decode($json,true);
$email = $obj['email'];
$sql = "SELECT id, name, email FROM Registration WHERE email='$email'";
$result = mysqli_fetch_array(mysqli_query($conn,$sql));
if (isset($result)) {
$result = array('result' => 0);
echo json_encode($result);
} else {
$result = array('result' => -1);
echo json_encode($result);
}
echo $json;
$conn->close();
?>
upd: I found out that in my console it shows:
Success
Array [
Object {
"contact_id": undefined,
"email": "Djdf",
"name": undefined,
},
]