Subject: Apology for Error in Crediting Payment — Prompt Payer Dear [Customer's Name], I hope this letter finds you in good health and high spirits. First and foremost, please allow us to extend our sincere apologies for the oversight regarding your recent payment. We have discovered an unfortunate error in our system that prevented us from properly crediting your payment for the invoice labeled [Invoice Number]. We deeply regret any inconvenience this may have caused and want to assure you that we take this matter seriously. As a valued customer and someone who has consistently exhibited prompt payment behavior, we understand the frustration and disappointment you may have experienced due to this oversight. We appreciate your loyalty and swift action in addressing the situation. Our dedicated team has now rectified the issue and ensured that your payment has been applied to your account effortlessly. It is important for us to emphasize that this incident was an anomaly and not reflective of the high standards we uphold at [Company Name]. Steps have been taken to prevent any recurrence of such errors in the future, including implementing additional checks and balances within our system. We understand that timely and accurate crediting of your payment is vital for your financial planning. Hence, we would like to offer our sincerest apologies, accompanied by a token of appreciation for your understanding and patience during this period of inconvenience. We will be crediting an additional [dollar amount or percentage off] towards your next invoice/payment. This gesture reflects our commitment to maintaining your satisfaction as a customer. Please rest assured that your prompt payment behavior has always been acknowledged, and we deeply regret the impact this one incident may have had on our relationship. We value your trust and loyalty, and we hope that you will give us a chance to make it right and restore your faith in our exceptional service. If you have any questions or require further information, please do not hesitate to reach out to our dedicated customer service team at [Phone Number] or [Email Address]. Our team stands ready to assist you with prompt and gracious service throughout this process. Thank you for your understanding and acceptance of our sincerest apologies. We are grateful for your continued support and look forward to serving you with excellence in the future. Warmest regards, [Your Name] [Your Title/Position] [Company Name]