bind_param is causing an error, what am i doing wrong? - php

Question

This is a project for school. I'm am trying to post to the database, but after I click on submit it comes back with an error about the line with bind_param:
Fatal error: Uncaught Error: Call to a member function bind_param() on boolean in /var/www/html/ticketsysteem/acties/nieuwTicket.php:42 Stack trace: #0 {main} thrown in /var/www/html/ticketsysteem/acties/nieuwTicket.php on line 42
Can somebody help me?
<?php
//var
$naam = trim($_POST["klantNaam"]);
$achternaam = trim($_POST["klantAchternaam"]);
$tel = trim($_POST["klantTel"]);
$adres = trim($_POST["klantAdres"]);
$postcode = trim($_POST["klantPostc"]);
$stad = trim($_POST["klantStad"]);
$email = trim($_POST["klantEmail"]);
//nieuwe klant
if (isset($_POST['submit1'])) {
$insertklant= $connectie->prepare("INSERT INTO klant klantAchternaam = $achternaam,
klantNaam = $naam, klantTel = $tel, klantAdres = $adres, klantPostc = $postcode,
klantStad = $stad, klantEmail = $email");
$insertklant->bind_param('sssssss', $achternaam, $naam, $tel, $adres, $postcode, $stad, $email);
if($insertklant->execute()) {
echo 'gelukt!';
}
}
?>
<form name="nieuwTicket" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>" method="POST">
<button onclick="nieuwek()" type="button" id="nk" >nieuwe klant </button>
<label class="hidden01">naam:</label><input id="text1" type="text" name="klantNaam" class="hidden"/><br>
<label class="hidden01">achternaam:</label><input id="text1" type="text" name="klantAchternaam" class="hidden"/><br>
<label class="hidden01">adres:</label><input id="text1" type="text" name="klantAdres" class="hidden"/><br>
<label class="hidden01">postcode:</label><input id="text1" type="text" name="klantPostc" class="hidden"/><br>
<label class="hidden01">woonplaats:</label><input id="text1" type="text" name="klantStad" class="hidden"/><br>
<label class="hidden01">telefoonnummer:</label><input id="text1" type="text" name="klantTel" class="hidden"/><br>
<input type="submit" name="submit1" value="invoeren" class="hidden">
</form>

Answer 1

Learn how to use prepared statements and what they actually do:
<?php
$stmt = $connectie->prepare("
INSERT INTO klant
klantAchternaam = ?,
klantNaam = ?,
klantTel = ?,
klantAdres = ?,
klantPostc = ?,
klantStad = ?,
klantEmail = ?
");
if($stmt){
$stmt->bind_param('sssssss', $achternaam, $naam, $tel, $adres, $postcode, $stad, $email);
if($stmt->execute()) {
echo 'gelukt!';
}
}
?>
Your current code is wide open to sql injection, while the above code is fully secured against them. The whole idea of prepared statements is that you never have to concat user submitted values directly to the sql query.