GPT-5.6 Luna vs Grok 4.5for writing emails

**Subject: Invoice #1042 – 21 days overdue**

Hi [Name],

I hope you’re well. As a valued long-standing client, we appreciate our relationship and wanted to follow up on invoice #1042 for **£1,840**, which is now 21 days overdue.

Could you please check its status and let us know if there’s anything holding up payment? We’d appreciate your prompt attention so we can keep our accounts up to date.

**Please arrange payment of £1,840 within the next five working days.**

Best,  
[Your Name]

Subject: Overdue Invoice #1042 – £1,840

Dear [Client Name],

I hope you're well. As a valued long-standing client, I wanted to gently follow up on invoice #1042 for £1,840, which is now 21 days overdue. We appreciate your continued partnership and know these things can sometimes slip through.

Could you please arrange payment by the end of this week or let me know if there’s any issue I can help resolve?

I look forward to sorting this quickly so we can carry on as usual.

Best regards,  
[Your Name]

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