How can I close the checkout window after a successful purchase?

[absltd]

Hi there. I'm using Buy It Now buttons on my own website. I don't use the Shopify store and haven't configured it. Everything works as it should - the cart and checkout load into a new browser window on top of my website. When customers make a successful purchase I want that browser window to close, but instead, my unconfigured Shopify store is loaded into the checkout window. Can I configure the checkout window to close?

[absltd]

I still haven't resolved this issue. Can anyone help please?