SQLSTATE[23000]: Integrity constraint violation: 1048 Column - php

Question

I am getting this error, i make sure all names are correct and idk what's wrong, seems like nothing is added in rsn column. Been searching around and i know issue but i don't know what is causing my issue and if you can comment my code if it's injectable, first time using PDO.
html
<form action="rsdenar.php" method="post">
<div id="gold-calc">
<div class="col-md-4">
<label for="amount"><h3><i class="fa fa-database"> Kolicina</i></h3></label>
<input type="text" class="form-control" id="amount" name="gpamount">
</div>
<div class="col-md-4">
<select class="form-control" style="margin-top:30px; width: 70%;" id="goldtype">
<option value="0.5">RS3</option>
<option value="1.6">RS 07</option>
</select>
</div>
<div class="col-md-4">
<label for="price"><h3><i class="fa fa-database"> Cena</i></h3></label>
<input type="text" class="form-control" id="price">
</div>
<div class="row" style="padding-top: 170px;">
<label for="idrsn">RSN: </label>
<input type="text" class="form-control" id="idrsn" name="rsn" style="width: 40%">
</div>
<div class="row">
<label for="emailbuy">Email: </label>
<input type="text" class="form-control" id="emailbuy" name="email-nakup" style="width: 40%;">
</div>
<div class="buy-order">
<button type="submit" class="btn btn-primary"><a style="text-decoration: none" href="#"><h5 style="font-family: arial; font-size: 20px">NAKUP</h5></a></button>
</div>
</div>
</form>
php
<?php
include 'php_includes/db_connect.php';
try {
$stmt=$conn->prepare("INSERT INTO purchase (rsn,email,amount,unique_id)
VALUES (:rsn, :email, :amount, :unique_id)");
$stmt->bindParam(':rsn', $_POST['rsn']);
$stmt->bindParam(':email', $_POST['email-nakup']);
$stmt->bindParam(':amount', $_POST['gpamount']);
$stmt->bindParam(':unique_id', $_POST['unique_id']);
$stmt->execute();
}catch (exception $e){
echo $e;
}
?>
sql

Answer 1

As your error states, Integrity constraint violation: 1048 Column 'rsn' cannot be null in, so you will need to always check if the value of rsn is empty before you try to insert the data on the table.
You can do this by this way on your PHP code:
<?php
// validation added here
if(isset($_POST) && !empty($_POST['rsn'])) {
try {
$stmt=$conn->prepare("INSERT INTO purchase (rsn,email,amount,unique_id) VALUES (:rsn, :email, :amount, :unique_id)");
$stmt->bindParam(':rsn', $_POST['rsn']);
$stmt->bindParam(':email', $_POST['email-nakup']);
$stmt->bindParam(':amount', $_POST['gpamount']);
$stmt->bindParam(':unique_id', $_POST['unique_id']);
$stmt->execute();
}catch (exception $e){
echo $e;
}
}