Dear Sir/ Madam,
Greetings of the day,
This is to request you to proceed with the pending payment of _________ (mention amount) which is due for ___________ (mention purpose – against invoice/order/ any other). It is to inform you that it has already been __________ (number of days) and the payment is not yet received.
It is to request you kindly proceed with the same at the earliest. In case of queries, you may contact at the contact details mentioned below.
__________ (Your name),
__________ (Contact details)