Let me join you here and help you make sure the sales transactions are sent out to your customers, dellabellap5.

I tried sending invoices with a Due on receipt term and I was able to email it successfully. 

This error might be caused by too much cache or an issue in the browser that you're using. I have steps to share that can resolve some of the most common browser and unexpected results when working in the program.

Let's start by switching or using other browsers like Google Chrome, Mozilla, Microsoft Edge, or Safari. They are all compatible with QBO and can help us isolate the issue. Use these keyboard shortcuts on how to do that:

• Ctrl + Shift + N for Google Chrome
• Ctrl + Shift + P for Firefox
• Control + Option +P if you're using Safari
• Ctrl + Shift + P for Microsoft Edge

After that, try to email an invoice to check if the error is no longer there. If everything is working fine,  follow the steps in this article on how to clear cached or delete internet files; Clear Cache and Cookies to Fix Issues When Using QuickBooks Online.

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