Script on first time invoice paid

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Hello,

 

Any idea how I can make it so I can run a script the first time the client pays for their product?

 

I've gotten use to the idea of action hooks and APi but was wondering what is the correct way to do this?

 

I can do this script on the hook (AfterShoppingCartCheckout), would it be best to save the scripts then execute once the invoice is paid for? As for the AfterShoppingCartCheckout will allow me to access more information about the order etc.

 

Thanks