This returns mysql_error:

<?php

$name = $_POST['inputName2'];
$email = $_POST['inputEmail2'];
$instruments = $_POST['instruments'];
$city = $_POST['inputCity'];
$country = $_POST['inputCountry'];
$distance = $_POST['distance'];

// ^^ These all echo properly ^^

// CONNECT TO DB
$dbhost = "xxx";
$dbname = "xxx";
$dbuser = "xxx";
$dbpass = "xxx";

$con = mysqli_connect("$dbhost", "$dbuser", "$dbpass", "$dbname");

if (mysqli_connect_errno())
{
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

$query = "INSERT INTO depfinder (name, email, instrument1, instrument2, instrument3, instrument4, instrument5, city, country, max_distance) VALUES ($name, $email, $instruments[0], $instruments[1], $instruments[2], $instruments[3], $instruments[4], $city, $country, $max_distance)";
$result = mysqli_query($con, $query) or die(mysqli_error($con)); // script fails here

if (!$result)
{
    echo "There was a problem with the signup process. Please try again later.";    
}

else
{
    echo "Success";
}
}
?>

N.B. I'm not sure whether it's relevant, but the user may not choose five instruments so some $instrument[] array values may be empty.

Bonus question: is my script secure enough or is there more I could do?