QB invoice won't let me send just states ERROR there was a problem adding this invoice, if the problem continues contact support

Hi there, Robbin.

In some cases, the invoice won't send because parts of the invoice were blank. Just ensure to put the necessary details from Customer name, Amount, Invoice, term, and item.

And if the information mentioned is there this might be a browser-related concern because of the large data cache. Thus, I recommend using a private browser and clearing the store cache to confirm if this is a browser-related issue. 

You can use the keyboard shortcuts below: 

• Google Chrome: press Ctrl + Shift + N
• Mozilla Firefox: press Ctrl + Shift + P
• Microsoft Edge: press Ctrl + Shift + N
• Safari: press Command + Shift +N

Then, try to send an invoice again. If it works, return to your regular browsing and clear the cache. If this doesn't work, try using another supported browser to know the cause of this product behavior.

And if the issue persists, I suggest reaching out to QuickBooks Online Support to help you pull up your account in a safe environment.

If you want to learn how to send invoices over time as you work off an estimate in QuickBooks, you can read this article: Set up and send progress invoices in QuickBooks Online.

Let me know how it goes so I can assist you further by replying to this thread or posting again in the Community. Solving your issue is our goal. Take care always, and have a good one!