To make your Completion payment login to your WeddingMix account. Then click on the link "Complete my Reservation" under your project name. You will be asked to put in the address you would like your cameras shipped to. When you are done click Next.
The next screen will have a link that will take you to Amazon payments. Complete your order through Amazon and look for an email titled "Your WeddingMix order is set! " from email@example.com. This email will have additional important information for you regarding your order.
If that link does not appear then you may have started your completion payment previously. Click on the project that reads "COMPLETE APP +<your package>" in the project name column and Started in the ordering column. This will take you through the payment process.