Let's ensure you can send invoices and get you back on business, Stevo.
First off, may I ask what specific error you've received? This way, we can give you the necessary troubleshooting you need. Any additional information will be much appreciated.
In the meantime, let's perform a browser troubleshooting to determine if this error is browser-related. QuickBooks may encounter errors due to accumulated cache.
We can start by logging into your account using a private browser. You can refer to these shortcut keys to open a private window in all supported browsers:
However, if the issue persists, I suggest contacting our QuickBooks Online Customer Support, for they have the necessary tools and expertise to investigate this further. To learn how to reach them, please refer to this article: Contacting QuickBooks Support.