How do solve this problem? Fatal error: uncaught pdoexception: SQLSTATE[HY093]: invalid parameter number

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PHP

//user.class.php
<?php
	
	Class User
	{
		private $errormessage = "";
		public function signup($POST)
		{
			$data = array();
			$db = Dbconnect::getInstance();
			$data['$user_firstname'] = trim($POST['sig_user_firstname']);
			$data['$user_lastname'] = trim($POST['sig_user_lastname']);
			$data['$user_email'] = trim($POST['sig_user_email']);
			$data['$user_pass'] = trim($POST['sig_user_pass']);
			$user_pass2 = trim($POST['sig_user_pass2']);
			$data['$user_phone_num'] = trim($POST['sig_user_phone_num']);

			if(empty($data['$user_email']) || !preg_match("/^[a-zA-Z_-]+@[a-zA-Z]+.[a-zA-Z]+$/", $data['$user_email']))
			{
				$this->errormessage .= "Please enter a valid email.";
			}
			if(empty($data['$user_firstname']) || !preg_match("/^[a-zA-Z]+$/", $data['$user_firstname']))
			{
			 	$this->errormessage .= "Please enter a valid first name.";
			}
			if(empty($data['$user_lastname']) || !preg_match("/^[a-zA-Z]+$/", $data['$user_lastname']))
			{
			 	$this->errormessage .= "Please enter a valid last name.";
			}
			if($data['$user_pass'] !== $user_pass2)
			{
				$this->errormessage .= "The password does not match.";
			}
			if(strlen($data['$user_pass']) < 5)
			{
				$this->errormessage .= "The password must be at least 5 characters long.";
			}
			if($this->errormessage == "")
			{
				
				$data['user_type'] = "customer";
				$data['user_id_url'] = $this->get_random_string(60);
				show($result);
				$query = "insert into user (user_id_url, user_firstname, user_lastname, user_email, user_pass, user_phone_num, user_type) values (:user_id_url, :user_firstname, :user_lastname, :user_email, :user_pass, :user_phone_num, :user_type)";
				
				$result = $db->write($query,$data);
				//show($result);
				if($result)
				{
					header("Location: ". ROOT ."login");
					die;
				}
			}
		}
		public function login($POST)
		{

		}
		public function get_user($url)
		{
			
		}
		private function get_random_string($strlen)
		{
			$ranArray = array('!','@','#','$','%','^','&','*','(',')',0,1,2,3,4,5,6,7,8,9,'q','w','e','r','t','y','u','i','o','p','a','s','d','f','g','h','j','k','l','z','x','c','v','b','n','m','Q','W','E','R','T','Y','U','I','O','P','A','S','D','F','G','H','J','K','L','Z','X','C','V','B','N','M');
			$rantext="";

			$strlen = rand(4,$strlen);
			for ($i=0; $i < $strlen; $i++) 
			{ 
				$rankey = rand(0,61);
				$rantext .= $ranArray[$rankey]; 
			}

			return $rantext;
		}
	}

//dbconnect.php
<?php
	//this is ensure that the website itself connects to the database
	Class Dbconnect
	{
		public static $conn;
		public function __construct()
		{
			try
			{
				$str = DB_TYPE . ":host=" . DB_HOST . ";dbname=" . DB_NAME;
				self::$conn = new PDO($str,DB_USER,DB_PASS);
			}
			catch (PDOException $error)
			{
				die($error->getMessage());
			}
		}

		public static function getInstance()
		{
			if(self::$conn)
			{
				//return self::$conn;
			}
 
			return $instance = new self();
		}
		public static function newInstance()
		{
			return $instance = new self();
		}
		//reading data from the database
		public function read($query, $data = array())
		{
			$statem = self::$conn->prepare($query);
			$result = $statem->execute($data);

			if($result)
			{
				$data = $statem->fetchAll(PDO::FETCH_OBJ);
				if(is_array($data))
				{
					return $data;
				}
			}
			return false;
		}
		//write data to database incl. delete/update
		public function write($query, $data = array())
		{
			$statem = self::$conn->prepare($query);
			$result = $statem->execute($data);

			if($result)
			{
				return true;
			}
			return false;
		}
	}

The error occurs when I tried to insert values into MySQL database

What I have tried:

I have tried changing the value names but no luck.