Shopify Post-Purchase Checkout Extension - How to get the order Id?

Shopify Partner
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I have created a basic Shopify post-purchase checkout extension, using this tutorial :

The buyer sees the post purchase page after they have placed an order and can add a product to their existing order. I want to know the order Id of the edited order, so I can tag it with my app's name.

I have not been able to find a way to get the order Id of the initial purchase. Need some help with this please!