How to communicate wiht clients ,when they request compensat

You cann't escape from the compensate, because it's your fault to delay.
First, Recognize the mistake and request understanding sincerely.
Second, Recognize your clinets' loss.
Third, according to the loss, you should afford it.
Maybe you will feel that you loss much just because of the little fault, but I want to remind you better late than never and misfortune may be an actual blessing.