[Your Name, & Address here]
[Recipient Name & address here]
We regret to inform you that we are holding back your payment for invoice [no.] until – [state condition for releasing payment]
– [Describe reasons in brief] –
So, unless you [condition for releasing payment], we will not release the payment.
Once you agree with the above mentioned, we will happily pay you in full.
Thank you for your consideration into this matter.
Encl: [Enclosures List here]