We'd really want to have this sorted out so you can send your invoices again, concrate1.

According to the latest updates, our engineers are still working on the investigation in relation to being unable to send invoices or reminders from QBO. Other customers have also reported having the same experience when emailing their sales transactions. 

In the meantime, you can continue with the workaround while this is being worked on. Rest assured that email communications will be sent out as soon as the issue is sorted out.
 

We appreciate your patience on this one. Let me know if you need anything else and I'd be glad to offer my help anytime you need it.