Understanding Order IDs
When a customer places an order on your BigCommerce store, that order is assigned a unique ID number. It is specific to that order and is never assigned again. This is to prevent confusion when customers do not finish the checkout process, and to ensure that payment gateways don't decline the order as a duplicate transaction.
By default, your first order will be Order ID 100. The Starting Order ID can be changed for accounting integrations, store migration or other reasons.
If a customer doesn't complete the checkout process, then their order will not appear in the control panel unless you change the order view to Incomplete Orders.
Order IDs may be deleted if the customer starts the checkout process over. This can happen if the customer clears their browser cache, closes their browser or temporarily loses their internet connection. Deleted Order IDs can explain gaps or skipped orders in your Order ID sequence. These instances are documented in Store Logs.