Billing occurs 30 days in arrears from the day that you completed your 14 day free-trial. For example if you completed your free trial on the 5th of November then your first bill is due on the 5th of December.
Your bill will be automatically deducted from the funds in your account balance. Once deducted you will see a transaction on the transaction table.
If you have integrated your accounting software with DiviPay then this bill will be automatically imported with the invoice attached.