When invoicing a customer, is there anyway that QB can notify me if I have used a customer purchase order number before, Like telling me it's a duplication?

Thanks for reaching out to us, Talos. 

I'm here to help you achieve your goal of detecting when a duplicate purchase order number is created. 

We can utilize the Custom Transaction Numbers feature by clicking the gear icon that appears when you're on the Purchase Order transaction screen. This will then enable QuickBooks to monitor for duplicate PO numbers entered automatically.

I'll provide screenshots for reference.

See this article for more details: Add custom transaction numbers to sales forms in QuickBooks Online

In addition, see these articles below about how to copy purchase orders to quote and customise sales forms:

• Copy a quote to a purchase order
• Customise invoices, quotes, and sales receipts in QuickBooks Online

I'm always here to listen and help if you have other QuickBooks concerns. Just post a reply below. Keep safe.

Thank you for your reply, but I don't think I made myself clear, sorry.

The customer gives me a purchase order on accepting my service, which they in return wants the PO nr to be added onto the invoice I'm giving them. I was wondering if there is a way that the QB system can alert me, when I use the customer's PO nr twice?

Let me step in and share some details about PO numbers Talos.

I recognize the importance of having the option to alert you that the PO number is already in use. However, this option is unavailable in QuickBooks Online (QBO). I recommend sending feedback to our development and product teams to actively monitor and consider user input in this channel when making decisions about product enhancements and feature reinstatement. 

1. In your QBO account, go to the Gear icon on the upper right side.
2. Click Feedback under Profile.
3. Type your suggestion in the box and tap Next.

Lastly, you can visit these articles to get more tips about handling sales and customers:

• Add, organize, and send invoices.
• Topics about your company's income and customers.

We aim to provide a more streamlined and user-friendly experience while also maintaining a set of features. If you have other concerns, please let me know by commenting below. I'm here whenever you need more details.