Dear Mr Brown
We have a very uncomfortable request – we are asking for an extension of time on our bill for ____ (amount).
We had been depending on a check from one of our clients to cover this bill. However, we have just been informed that this check will not arrive until _______ (date).
Therefore, we must ask for your indulgence and grant us a two weeks’ extension of time on our bill. We are sorry about any inconvenience this may bring to you.