Woocommerce product with price from JSON

In essence what I need is someone to be able to click a button on another website that “knows” the price and somehow lets my site learn it, add it to cart and order it.

Here is what I am trying to do: A fellow site makes a request to my site like this:
http://example.com/?add-to-cart=14&REQ&id=32&key=6337

Then if the REQ parameter exists, I crosscheck with a separate database to see the price in a table row where theID and KEY match. Then I use this price to add the custom product to cart.

And here is the code as a separate plugin after seeing this solution:

add_filter( 'woocommerce_add_cart_item' , 'set_woo_prices');
add_filter( 'woocommerce_get_cart_item_from_session', 'set_session_prices', 20 , 3 );

function set_woo_prices( $woo_data ) {
    $w_price = 999.99;
    if (isset($_GET['REQ'])) {
       $w_id = $_GET['id'];
       $w_key = $_GET['key'];
       //we ask the database
        $my_wpdb = new WPDB( 'rt', 'rt', 'db', 'localhost');
        $curr_req = $my_wpdb->get_row( "SELECT * FROM tbl WHERE id = $w_id", ARRAY_A );
        if ( $curr_req['keypin'] == $w_key ){
           $w_price = $curr_req['price'];
            }
        else {
           exit;
       }
        $woo_data['data']->set_price( $w_price );
        $woo_data['my_price'] = $w_price;
        return $woo_data;
       }
    };
function  set_session_prices ( $woo_data , $values , $key ) {
    if ( ! isset( $woo_data['my_price'] ) || empty ( $woo_data['my_price'] ) ) { return $woo_data; }
    $woo_data['data']->set_price( $woo_data['my_price'] );
    return $woo_data;
};

But no… Of course it wouldn’t work:

• If I add to cart for the first time and the ID and KEY match, I get the proper price and I’m good. If I delete the product from the cart, and re-add it with different ID, KEY and thus Price, it takes the previous price or the original from the product.
• If I try to add any product to cart without the parameters it’s not added. If I deactivate the plugin, it works.

For the love of God, I cannot understand what is wrong with the above code. I assume there must be something with the session but this would only explain the first point.

Any ideas, help are highly appreciated and needed. Even if I’m in a completely wrong direction.

I’m not sure I get it right but if you mean the part “and re-add it with different ID…”, yes, I add it in the same way just using different ID & KEY in order to have a different price.

Can I somehow pinpoint this to just product with ID 14; so at least all other products can be untouched?

Is it the right direction at all or is it better to find another way?

Thank you Mike, I added an else statement which returns the $woo_data
This saved the normal add to cart.

What works horribly inconsistently though is -after clearing all sessions- when I try to add the product from scratch through this URL it tries to add it multiple times (have chosen sold individually) and prices are wrong. I do believe that something is wrong on the session part.

Should I maybe use the hook woocommerce_get_price instead?