I guess if you've stumbled upon this post it means that you're having some trouble with the Shopig checkout or add to cart process and you're seeing this error
Required parameter missing or invalid: id
Generally this error can show for a few different reasons:
- You're trying the checkout to the wrong address
- You're trying to add to cart, but again - to the wrong address
- You're trying to add to cart and you've not got a form element with a product ID
In all cases check your code and make sure that no only are you posting to the correct address but you're also sending along the required data as well.