Send Purchase Order reminder messege

What should I write?!

[Khara]

Hi, I want to send reminder email to my customer to remind him pay the Purchase Order that he placed it without pay it before about month. Actually English is not my first anguage so anyone can help me how to write this email?

Thank you for your help.
Regards.

[Essex_boy]

Dear Sir

Re: Unpaid purchase order.

Pay up or die the death of a thousand cuts.

Thank you.

[Khara]

Essex_boy
this is not a series thread so please keep it series

[DamonHD]

Dear Sir

Re: Unpaid purchase order.

We have not received your payment of XXXX by the agreed date YYYY, so we would appreciate immediate payment by return.

Thank you.

[Essex_boy]

Sorry Khara

[Khara]

thank you DamonHD.