Avviso:mysqli_stmt::bind_param():il numero di variabili non corrisponde al numero di parametri nell'istruzione preparata

Hai perso le virgolette intorno a ? e usa 10 parametri invece di 11

Invece di questo:

$insert = "INSERT INTO record_user (ip,country,address,stack,skills,employment_type,city_selection,landing_time,submission_time,time_spent) 
VALUES ('?','?','?','?','?','?','?','?','?','?')";
$insert = $con->prepare($insert);
$insert->bind_param("ssssssssss", $user_ip, $country, $location, $stack, $skills, $employment, $city, $landing_time, $submission_time, $time_spent);

Prova questo:

$insert = "INSERT INTO record_user (ip,country,address,stack,skills,employment_type,city_selection,landing_time,submission_time,time_spent)
VALUES (?,?,?,?,?,?,?,?,?,?)";
$insert = $con->prepare($insert);
$insert->bind_param("ssssssssss", $user_ip, $country, $location, $stack, $skills, $employment, $city, $landing_time, $submission_time, $time_spent);