Once you have validated, ensure that there are no errors.
You can then process the billing as per the "Process Billing" menu item. If your Billing Cycle validated successfully (without any errors, warnings is ok), the relevant Billed Cycle will be in the "Select a billing cycle to process" drop-down. Select the Billing Cycle and select "Process Billing". Varibill then validates your billing data again to ensure no new records were added or entities changed. Once this is done each clients' invoice/s will be generated.
Once the billing processing is complete the invoice/s generated can be viewed by navigating to Finance --> Invoices.
Refer to this article on docs.varibill.com for more information on the billing process.