Here are three different styles for a demand email — direct, firm, high-consequence language, speaking like someone who's done it before.

Style 1 - Straight to the Point

Dear [Client name],

We've followed up several times over the past weeks about the outstanding payment of [$10,000] for our work at [123 Street Name, Los Angeles, CA 91234]. I truly hope there's no issue on your end. We're only asking for final payment for the approved amounts.

If you could arrange the full amount by this Friday, we'd greatly appreciate it. [optional: Otherwise, I'm afraid we'll have to move forward with filing a lien... not something either of us wants.] Let's sort this promptly.

Thank you,

[Your name]

Style 2 - More legal

Dear [Client First Name],

We requested payment multiple times, and have now reached a point where it feels like the conversation has stopped being productive.

We have an outstanding payment of [$10,000] for labor and materials supplied to your project at [Project Address] under our agreement dated [date]. This email constitutes formal demand for full payment within 7 calendar days.

[optional: If payment is not received promptly, we will proceed recording a mechanic's lien, without further notice.] We hope you can help resolve this.

Regards,
[Your Full Name]

Style 3 - More funny, and blaming the office

Dear [Client],

Our accounts department has been attempting to resolve the outstanding balance of [$10,000] for several weeks. Despite repeated follow-up messages, we have not yet received payment for work completed, accepted, and incorporated into the project at [Project Address].

We are requesting only what was expressly agreed upon in our contract—no additional charges, no penalties (at this point), simply the amount due for services rendered.

If payment in full can be arranged by the close of business this Friday, the matter will be closed without further escalation. [optional: Should that not occur, we will have no choice but to proceed with the recording of a mechanic’s lien.]

I would prefer we avoid that step. It is an administrative inconvenience for everyone involved.

Please let us know if payment can be settled by end of week.
Thank you for your attention to this.

[Your name]