Warning: Undefined array key "post_id" in C:\xampp\htdocs\API\reply.php on line 13

Fatal error: Uncaught mysqli_sql_exception: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 8 in C:\xampp\htdocs\API\reply.php:23 Stack trace: #0 C:\xampp\htdocs\API\reply.php(23): mysqli->query('SELECT\r\n ...') #1 {main} thrown in C:\xampp\htdocs\API\reply.php on line 23