Pinterest Tag on checkout page

Is it possible to place my Pinterest tag and "add-to-cart" event code on the checkout page? I would like the event to fire on the url:  www.mydomain.com/checkout.  I already tried the code injection page (where I was able to add my Pinterest tag and "checkout" event code on the order confirmation page).  I would like to be able to retarget users who added items to the cart, but didn't checkout.  Thank you for your help!

Same! Have you been able to figure this out?

I keep getting error messages that the tags are not firing.