There will be a new option under the invoicing setup page. The "Require Payment before Approval" will allow a Request to not be fully approved until an Invoice is paid.
When selecting the number of Days, the Invoice is due there will be two options. "Before First Event Date" will ensure you receive a payment before the event. Or you can choose From "Invoice sent Date."
A separate status will be available stating "Awaiting Payment." Once the payment is received, the Request will then be fully approved.
If you have any additional questions or concerns, please feel free to submit a support ticket at: http://support.mlschedules.com/support/home