PHP Warning: mysqli::query(): Couldn't fetch mysqli [duplicate]

Answer 1

This:

$addshort = $conn->query("INSERT ...')");
^^^^^^^
if ($conn->query($addshort) === TRUE) {
                   ^^^^^

$addshort is your query result/handle/object, which you then try to EXECUTE AGAIN, which doesn't work. query() expects an SQL string, and you're passing in an object.

And on top of that, you're vulnerable to sql injection attacks.

Answer 2

Your connection has been closed, after execution of first SELECT Statement, it means connection closed to early:

$conn->close();

You need to use close() after your all queries or re build connection. ist one is the better option.

You are getting user input $_REQUEST['key'], it means your query is open for SQL injection, this will help you to understand how can you prevent your code with SQL injection: How can I prevent SQL injection in PHP?