PHP - Converting elements to actual values

Question

I made a list of checkboxes that upon click would be sent to database. Every time I submit data the value is 0. If I try and convert the value of the array to string, I get string to array error.

<form method="post">
<?php

global $wpdb;

$Result = $wpdb->get_results("SELECT Product1 FROM A");

foreach($Result as $Thing1) {
    echo '<input type="checkbox" name="Num1[]" />' . $Thing1->Product1 . "<br />";
}
    $Age = $_POST['Num1'];

if($_POST['btn']) {
    if(!empty($Age)) {
        foreach($Age as $id) {
         // this enters in the value as 0 idk why
        $wpdb->query("INSERT INTO A(Product1) VALUES('$id');");
        }
        
     }
}

?>

<button name="btn">Submit</button>
</form>

Answer 1

You didn't include value in your checkboxes you have:

'<input type="checkbox" name="Num1[]" />' . $Thing1->Product1 . "<br />";

Should be:

'<input type="checkbox" name="Num1[]" value="' . $Thing1->Product1 . '" />' . $Thing1->Product1 . "<br />";