Api - Shipments Question

I am using http://docs.cs-cart.com/4.1.x/api/entities/shipments.html and the cscartapi routine from https://github.com/drahosistvan/cscartapi and help from http://forum.cs-cart.com/topic/44049-cs-cart-api-post-shipment-issue/?hl=api+shipments#entry245707

All seems to be working until I try and create a shipment for an order.

I have

...
try {
	$params = array(
			'carrier' => "UPS",									
			'order_id' => $order_id,
			'shipping_id' => "7",
			'shipping' => "UPS Test",
			'products' => '{"3450498700": "1"}',
			'tracking_number' => "1ZW812Y24298150999",								
							);  

$shipment = $cscartapi->create(“shipments/”, $params);

} catch (Exception $e) {
print $e->getMessage();
}

and I keep getting

"Message from CS-Cart API: Bad Request: Products for shipment were not selected"

I do not know what I am doing wrong.

$order_id is populated with the order_id, 3450498700 is the cart item ID for the ordered product and 1 is the qty. Only one product in this order

Please help

CS-Cart 4.3.4

I am not sure, but try to use

$params = array(
    'carrier' => "UPS", 
    'order_id' => $order_id,
    'shipping_id' => "7",
    'shipping' => "UPS Test",
    'products' => array(
        "3450498700" =>  "1",
    ),
    'tracking_number' => "1ZW812Y24298150999", 
);  

instead of:

$params = array(
    'carrier' => "UPS", 
    'order_id' => $order_id,
    'shipping_id' => "7",
    'shipping' => "UPS Test",
    'products' => '{"3450498700": "1"}',
    'tracking_number' => "1ZW812Y24298150999", 
);  

That worked, thanks. I'll let you know if I have any further questions.

David