逾期付款的委婉提醒技巧 — 国际贸易填空题

买方公司对发票 No.1043 的货款已逾期约一周，出口商拟发首封催款函。为体现委婉提醒技巧，函中不宜直接指责客户失信，而应假定对方付款延误出于无心之失。请补全下函中最恰当的委婉表达：Dear Sirs, We would like to remind you that Invoice No.1043 for USD 8,600 has been outstanding since March 15. We trust that this non-payment is merely a(n) ____ on your part, and we would appreciate it if you could let us have your remittance at your earliest convenience.