if (!class_exists('Updraft_Checkout_Embed')) include_once (UPDRAFTPLUS_DIR.'/includes/checkout-embed/class-udp-checkout-embed.php');
global $udp_checkout_embed;
$udp_checkout_embed = new Updraft_Checkout_Embed(
	'updraftplus'
	$data_url, 
	$load_in_pages
);

Params:

$plugin_name: (string) Current plugin using the class
$proructs_data_url: (string) url of the merchand website (eg: https://https://updraftplus.com)
$load_in_pages: (array) pages on which the script + css will be loaded

Cache:

The products data is cached and expires after 7 days. To force fetching it, add udp-force-product-list-refresh=1 to the admin page url

Using in the admin

Once the php is setup, you can configure the links / buttons in the admin.

Add data-embed-checkout="{$url}" to any link. eg:

global $updraftplus_checkout_embed;

$link_data_attr = $updraftplus_checkout_embed->get_product('updraftpremium') ? 'data-embed-checkout="'.apply_filters('updraftplus_com_link', $updraftplus_checkout_embed->get_product('updraftpremium')).'"' : '';

<a target="_blank" title="Upgrade to Updraft Premium" href="<?php echo apply_filters('updraftplus_com_link', "https://updraftplus.com/shop/updraftplus-premium/");?>" <?php echo $link_data_attr; ?>><?php _e('get it here', 'updraftplus');?></a>

On completion (when the order is complete), the event 'udp/checkout/done' is triggered.
The event 'udp/checkout/close' is triggered when the user closes the modal, regardless of success.

Use this to do something with the data received:

$(document).on('udp/checkout/done', function(event, data, $element) {
	// ... do something with data, currently data.email and data.order_number
	// $element clicked to open the modal.
});