As a Merchant, your 'Invoices' tab would contain the invoice from the Gateway. This could include a monthly fee, along with any additional transactional charges. Within this tab you have the abililty to pay the invoices via a card payment, along with downloading a copy of the invoice in a PDF format.
A full overview of this tab is detailed below:
Invoice Reference: This is the reference number found on the invoice PDF. When clicked upon you'll be able to download a PDF version of your invoice.
Action: You can use this button to pay your invoice via card payment.
Payments: View payments made against this invoice.
Bill Calculations: This shows how your bill total was calculated
Invoice Date: The billing date of the invoice.
Transactions: The number of transactions made within the billing period (Shown in Transactional Dates).
Transactional Cost: The total cost of your monthly transactions.
Flat Rate: The standard recurring fee (Paid in advance).
Total: The invoice total.
Total Paid: The total amount paid so far (and last method of payment).
Overdue: Whether the invoice has been marked as overdue.
State: Whether the invoice has been paid or not.