Subject: Request for Official Proof of Payment

Dear [Provider's Name],

I hope this message finds you well.

I am writing to follow up on the attached invoice, which appears to be unsigned and unstamped. To ensure that the payment has indeed been processed, I kindly request an official proof of payment for this invoice, as it pertains to a significant amount.

Your assistance in providing this documentation at your earliest convenience would be greatly appreciated. Thank you for your attention to this matter.

Best regards,

[Your Name]
[Your Position]
[Your Company]
[Your Contact Information]