Plugin Options not saving options and doesn't work

Question

So I've been making a plugin for wordpress that adds a custom post type for products, which was fairly simple and i made that work.

Afterwards I wanted to make a settings page sub menu to the custom post type in the admin menu and then create some options.

So the first problem i encountered was that a warning showed up that said

Warning:  Illegal string offset 'option1' in C:/blablablal on line 96

And from what I understand that means that the option doesn't know that it's supposed to save the options in an array but tries to put it in a string instead. So I found a way to make the warning go away by adding brackets to the variable.

$kns_options[] = get_option('kns_products_options');

(I don't know if this is a solution or not, but I couldn't find anything about it on loads of google searches)

So after the warning went away, I started to try and add options via the form I've created, but the options just don't want to save. I've tried to var_dump the variable, but it comes out empty.. Is there a typo somewhere, because i sure as hell can't find it!

I'll post the code below, please tell me if i should repost it in pastebin or something!

<?php
add_action( 'init', 'kns_register_products_post_type' );

function kns_register_products_post_type() {
    // Registrerar en custom post type som heter produkter
    register_post_type('produkter',
    array(
        'labels' => 
            array(
                'name' => 'Produkter',
                'singular_name' => 'Produkt',
                'add_new' => 'Lägg till ny',
                'add_new_item' => 'Lägg till ny Produkt',
                'edit_item' => 'Ändra Produkt',
                'new_item' => 'Ny Produkt',
                'view_item' => 'Visa Produkt',
                'search_items' => 'Sök Produkter',
                'not_found' => 'Inga produkter hittades',
                'not_found_in_trash' => 'Inga produkter hittades i papperskorgen',
                'parent_item_colon' => 'Produkt Förälder:',
                'menu_name' => 'Produkter'
            ),
        'public' => true,
        'supports' => array('title', 'editor', 'thumbnail'),
        'taxonomies' => array('category'),
        'menu_position' => 20,
        )
    );

}

add_action( 'admin_menu', 'kns_products_create_settings_submenu' );

function kns_products_create_settings_submenu() {
    // Skapar sub menu för Produkter-fliken
    add_submenu_page('edit.php?post_type=produkter', 'Inställningar', 'Inställningar', 'manage_options', 'product_settings', 'kns_products_settings_page' );
    // Kallar på register_setting funktionen
    add_action( 'admin_init', 'kns_products_register_settings');
}

function kns_products_register_settings() {
    register_setting( 'kns_products_settings_group', 'kns_products_options', 'kns_sanitize_options');
}

function kns_sanitize_options( $input ) {
    $input['option1'] = sanitize_text_field( $input['option1'] );
    $input['option2'] = sanitize_text_field( $input['option2'] );
}

function kns_products_settings_page() {
?>  
<div class="wrap">
<h2>Produktinställningar</h2>

<form method="post" action="options.php">
    <?php 
    settings_fields( 'kns_products_settings_group' );
    $kns_options[] = get_option('kns_products_options'); 
    var_dump($kns_options);
    ?>
    <table class="form-table">
    <h3>Utseende</h3>
        <tr valign="top">
            <th scope="row"><label for="option1">Blajja</label></th>
            <td>
                <input type="text" id="option1" name="kns_options[option1]" value="<?php echo esc_attr( $kns_options['option1'] ); ?>" />
            </td>
        </tr>
        <tr valign="top">
            <th scope="row"><label for="option2">Annan Blajja</label></th>
            <td>
                <input type="text" id="option2" name="kns_options[option2]" value="<?php echo esc_attr( $kns_options['option2'] ); ?>" />
            </td>
        </tr>
    </table>
    <p class="submit">
        <input type="submit" class="button-primary" value="Spara inställningar" />
    </p>

</form> 
</div>
<?php
}
?>

I really need help, I've been at this for hours now..

EDIT:

var_dump results are

array(1) { [0]=> string(0) "" } 

Answer 1

You aren't returning data from the sanitize function:

function kns_sanitize_options( $input ) {
    $input['option1'] = sanitize_text_field( $input['option1'] );
    $input['option2'] = sanitize_text_field( $input['option2'] );
}

There is therefore nothing to save. Try:

function kns_sanitize_options( $input ) {
    $input['option1'] = sanitize_text_field( $input['option1'] );
    $input['option2'] = sanitize_text_field( $input['option2'] );
    return $input;
}

Secondly, you've registered the name of your options as kns_products_options

register_setting( 'kns_products_settings_group', 'kns_products_options', 'kns_sanitize_options');

But you are using kns_options in the form.

<input type="text" id="option1" name="kns_options[option1]" //...

The API doesn't know how to find the data so $input in your sanitization callback is always null. Make that name attribute match the name you registered.

<input type="text" id="option1" name="kns_products_options[option1]" //...