The customer bills the order after the Item Fulfilment process. However, some Sales Orders show the Bill button on its page and are already listed on the Bill Sales Orders Page even they are still on Pending Fulfillment status.
Verified that the Invoice in Advance of Fulfillment = F under Setup > Accounting > Accounting Preferences > Order Management > Invoicing section.
Sales orders in question may contain Service for Sale items or other Non-Inventory items that have the Can be Fulfilled/Received checkbox under the Preferences tab unchecked. If this is not checked, this means that these items do not require being received and fulfilled, and can be billed immediately.
Possible Action: Customize the Bill Sales Order page and filter the Sales Orders by Pending Billing or Pending Billing/Partially Fulfilled Status.
1. Navigate to Transactions > Sales > Bill Sales Order.
2. Click Customize button under Orders Tab.
3. Click on Additional Filters Tab and check the Include checkbox beside Status
4. Click Save
5. Notice the Status filter under Orders Tab. You may now want to set it to Pending Billing or Pending Billing/Partially Fulfilled Status.