A Pre-Order credit is a product you can add to your pre-order price lists, that when purchased, will add an account credit to the customer's account. Then this credit can be used to purchase products when the photos are ready.
These can be created in Photo Products - Product Base (Create New Pre-Order Credit Button at the top) and are added to the price lists like all other photo products.
Create Product Name
The product name displayed to the customer
SKU
A reference name only shown to you
Price
The price they are paying for the credit
Credit Amount
The amount of credit applied to their account.
The credit amount can be different from the price. Example: You can offer a $25 account credit for $20.