Login Registration User Existance

UserExist.php

<?php 
//phpdark.com
//[email protected]
if (isset($_POST['login'])) {

	$con = new mysqli("localhost","root","","database"); //database connection
	if ($con) {
		$username = mysqli_real_escape_string($con, $_POST['$username']);
		$password = mysqli_real_escape_string($con, $_POST['$password']);
		$hashed_password = password_hash($password, PASSWORD_DEFAULT);

		

		if (empty($username) || empty($password) ) { //check wheather it is empty or not
			echo "Field must not be empty";
		} else {
			$sql = "select * from table where username='$username'";
			$check = $con->query($sql) or die($con->error)." error at line number ".__LINE__;
			if ($check) {
				$row = $check->num_rows;
				if ($row > 0) {
					echo "User already exist in database";
				} else {
					$sql = "select * from table where username='$username' and password='$password'";
					$stmt = $con->query($sql) or die($con->error)." error at line number ".__LINE__;

					if ($stmt) {
						$row = $stmt->num_rows;
						if ($row > 0) {
							$database_pass = $stmt->fetch_assoc()['password'];
							if (password_verify($database_pass, $hashed_password)) {
								
								session_start();
								$_SESSION['login'] = true;
								$_SESSION['username'] = $username;
								header("location: index.php"); //after successful login
							}
							
						}
					} else {
						echo "Failed to login";
					}
				}
			}

		}
	} else {
		echo "Database connnection failed";
	}

	

} 

Please this code is very wrong.... this is a wrong method of doing this.. please use a prepared statement... if it's going on production

thanks for sharing idea