Warning: Undefined array key "user_id" in /code/public/facturas.php on line 7

Fatal error: Uncaught mysqli_sql_exception: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 in /code/public/facturas.php:8 Stack trace: #0 /code/public/facturas.php(8): mysqli_query() #1 {main} thrown in /code/public/facturas.php on line 8