Notice: Undefined variable: email in /Applications/XAMPP/xamppfiles/htdocs/menthor/login.php on line 16 – Phpmyadmin

When signing into to the app with username, the email is not used hence the following error is throw and vice versa “Notice: Undefined index: email in /Applications/XAMPP/xamppfiles/htdocs/menthor/login.php on line 16”

I’ve tried putting the lines that were generating the error in conditions but those efforts proved futile
Login.php file(parts relevant to the error)

// STEP 1. Receive data / info paassed to current file
if ((empty($_REQUEST['username']) || empty($_REQUEST['password'])) && (empty($_REQUEST['email']) || empty($_REQUEST['password']))) {
    $return['status'] = '400';
    $return['message'] = 'Missing requird information';
    echo json_encode($return);
    return;

} 


// securing received info / data from hackers or injections
$email = htmlentities($_REQUEST['email']);
$username = htmlentities($_REQUEST['username']);
$password = htmlentities($_REQUEST['password']);

// STEP 2. Establish connection with the server
require('secure/access.php');
$access = new access('localhost' , 'root', '' , 'menthor');
$access->connect();

// STEP 3. Check existence of the user. Try to fetch the user with the same email address
// STEP 3. Check availability of the login/user information
$username_aval = $access->selectUser_Username($username);
$email_aval = $access->selectUser_Email($email);

//$return = array();

// user is found
if ($username_aval) {

    // Get encrypted password and salt from the server for validation
    $encryptedPassword = $username_aval['password'];
    $salt = $username_aval['salt'];

    if ($encryptedPassword == sha1($password . $salt)) {

        $return['status'] = '200';
        $return['message'] = 'Successfully Logged In';
        $return['id'] = $username_aval['id'];
        $return['username'] = $username_aval['username'];
        $return['email'] = $username_aval['email'];
        $return['fullName'] = $username_aval['fullName'];
        $return['lastName'] = $username_aval['lastName'];
        $return['birthday'] = $username_aval['birthday'];
        $return['gender'] = $username_aval['gender'];
        $return['cover'] = $username_aval['cover'];
        $return['ava'] = $username_aval['ava'];
        $return['bio'] = $username_aval['bio'];
        $return['allow_follow'] = $username_aval['allow_follow'];

    } else {

        // In event that encrypted password and salt does not match
        $return['status'] = '201';
        $return['message'] = 'Password do not match';

    }

} else if ($email_aval) {

    // Get encrypted password and salt from the server for validation
    $encryptedPassword = $email_aval['password'];
    $salt = $email_aval['salt'];

    if ($encryptedPassword == sha1($password . $salt)) {

        $return['status'] = '200';
        $return['message'] = 'Successfully Logged In';
        $return['id'] = $email_aval['id'];
        $return['username'] = $email_aval['username'];
        $return['email'] = $email_aval['email'];
        $return['fullName'] = $email_aval['fullName'];
        $return['lastName'] = $email_aval['lastName'];
        $return['birthday'] = $email_aval['birthday'];
        $return['gender'] = $email_aval['gender'];
        $return['cover'] = $email_aval['cover'];
        $return['ava'] = $email_aval['ava'];
        $return['bio'] = $email_aval['bio'];
        $return['allow_follow'] = $email_aval['allow_follow'];

    } else {

        // In event that encrypted password and salt does not match
        $return['status'] = '202';
        $return['message'] = 'Password do not match';

    } 
}else {

        // In event that user is not found
        $return['status'] = '403';
        $return['message'] = 'User was not found';

}

// stop connection with server
$access->disconnect();

// pass info as JSON
echo json_encode($return);

Access.php file(parts relevant to error)
Will try to select any value in the database based on received Email

public function  selectUser_Email($email) {

    // array to store full user related information with the logic: key=>Value
    $returnArray = array();

    // SQL Language / Commande to be sent to the server
    // SELECT * FROM users WHERE email='[email protected]'
    $sql = "SELECT * FROM users WHERE email='" . $email . "'";

    // executing query via already established connection with the server
    $result = $this->conn->query($sql);

    // result isn't zero and it has least 1 row / value / result
    if ($result != null && (mysqli_num_rows($result)) >= 1) {

        // converting to JSON
        $row = $result->fetch_array(MYSQLI_ASSOC);

        // assign fetched row to ReturnArray
        if (!empty($row)) {
            $returnArray = $row;
        }
    }

    // throw back returnArray
    return $returnArray;
}

// Will try to select any value in the database based on received Email
public function  selectUser_Username($username) {

    // array to store full user related information with the logic: key=>Value
    $returnArray = array();

    // SQL Language / Commande to be sent to the server
    // SELECT * FROM users WHERE username='rondell'
    $sql = "SELECT * FROM users WHERE username='" . $username . "'";

    // executing query via already established connection with the server
    $result = $this->conn->query($sql);

    // result isn't zero and it has least 1 row / value / result
    if ($result != null && (mysqli_num_rows($result)) >= 1) {

        // converting to JSON
        $row = $result->fetch_array(MYSQLI_ASSOC);

        // assign fetched row to ReturnArray
        if (!empty($row)) {
            $returnArray = $row;
        }
    }

    // throw back returnArray
    return $returnArray;
}

Current results when logging in via web server

Notice: Undefined index: email in /Applications/XAMPP/xamppfiles/htdocs/menthor/login.php on line 16
{"status":"200","message":"Successfully Logged In","id":"44","username":"rondell","email":"[email protected]","fullName":"rondell","lastName":"","birthday":"","gender":"","cover":"","ava":"","bio":"","allow_follow":"1"}

Expected Results

{"status":"200","message":"Successfully Logged In","id":"44","username":"rondell","email":"[email protected]","fullName":"rondell","lastName":"","birthday":"","gender":"","cover":"","ava":"","bio":"","allow_follow":"1"}