We're aware of the issue of getting an error when sending invoices. Our engineers found out that the issue is with the third-party email provider and they're working on the solution. While waiting for the fix, please continue to use all available features, including manually downloading the invoices and sending them from outside of QuickBooks, as a workaround.
On the other hand, I encourage you to contact our Support team so you will be added to the list of affected users for immediate updates. They have the tools on their end.
Go to Helpand select theSearchtab.
ClickContact Usat the bottom.
Enter something like getting a delivery error when sending invoices and click Continue.