How can i invoice a person who is also a supplier to me?, it appears not to let me.

Hi there, Alecohs.

I'd like to share some insights about creating an invoice in QuickBooks Online.

Each transactions in QuickBooks Online has its own functionality and follows a simple workflow. That being said, an invoice is sales form that can be used for customers if you plan to get paid in the future for products and services you sell.

You can create a customer profile for your supplier. This way, you can create and send them an invoice.

Like this: 

1. Go to the Sales menu.
2. Choose Customers tab.
3. Select Add customer manually.
4. Enter your customer's information.
5. Click on Save.

Here's an article for more details about the forms in QuickBooks Online: Description of QuickBooks Online forms.

Get back to me if you still have other questions about sales forms. I'll be in touch. Have a great day!