I cant send invoices, it's saying the delivery fails. Email is correct and I've sent them before, this just started yesterday

Hi there diamondoasis-sk-,

It's important that all your transactions be entered correctly so that your books can be well balanced. QuickBooks Online is a great tool able to help you create and send invoices to your customers so they know the amount owed to you for your services. I can point you in the right direction for assistance with delivery errors when sending transactions like invoices.

To resolve errors when sending invoices to your customers, I recommend trying the steps in this article to ensure that all is set up properly for emailing transactions. If the error is still present after that, I recommend reaching out to the support team outside the Community. They'll be able to view the error with you in a secure location so that you can send this transaction, or notify the engineers of the error if it still persists after further troubleshooting steps. You can reach them with these steps:

Schedule a Callback or start a Chat: click (?)Help in the upper right > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat.
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If you have any other questions, feel free to reach out here.