Dear [Supplier]
My next payment for [account AC1234XX; product; our lease] will be due at the end of this month on [date]. However, due to an unexpected company emergency, I will not be able to fulfill this obligation at this time. As a result, I am requesting an extension of [10 days] to make this payment by [date].
If you review my file, I believe you will find that my payments have [always; generally] been made in a timely fashion. My relationship with your [bank; firm] is very important to me, as well as my desire to maintain a good credit rating.
Thank you very much for your consideration of this request.