If a regional administrator fails to pay the amount billed by a statement submitted pursuant to section 230.20 within forty-five days from the date the statement is received by the regional administrator, the department shall charge the delinquent regional administrator the penalty of one percent per month on and after forty-five days from the date the statement is received by the regional administrator until paid. Provided, however, that the penalty shall not be imposed if the regional administrator has notified the department of error or questionable items in the billing, in which event, the department shall suspend the penalty only during the period of negotiation.