Hi First name,
I am writing to sincerely apologize for missing the deadline for the [Project].
I realize that my failure to meet the deadline has disrupted your schedule and may have caused inconvenience to our team - and I am really sorry for that.
I underestimated the time required to complete the project, which led to this delay.
I take full responsibility for this mistake and assure you that this is not indicative of my usual work ethic or commitment.
To rectify this situation, I have already re-prioritized tasks and worked overtime to get everything done. I am also implementing a more effective time management and project planning strategy to prevent such issues in the future.
I value our professional relationship and am committed to restoring your confidence in my abilities. Please let me know if there's anything else I can do to resolve this matter.
Thank you for your understanding and patience. I am looking forward to continuing our work together with renewed diligence.
Sincerely,
Ed Sheeran