Dear
Mr. Barnard,
Thank you very much for your invitation.
I love your idea of having dinner together at 6:00 next Monday afternoon. I'll be available that day and will be present on time./Unfortunately, I'll pay a visit to my clients that day. Could it be possible for you to change the schedule? I'll be available next Tuesday. I would be grateful if you could change the arrangement.
I look forward to meeting you soon.
Your sincerely,
Steve McCormack