With PLoS we have made an arrangement for a monthly billing. Therefore you should not receive invoices from PLoS. If you have published with PLoS and your article is listed on the monthly invoice, we will contact you and ask for a cost account / project number of you, that covers 50% or 60% of the APCs.
If you nevertheless receive an invoice, please don't pay it and send the invoice to us. We will try to tranfer the charges to the monthly billing.