I can imagine what you feel when encountering an issue when printing invoices in QuickBooks Online, @sie-electrical. Let me help you get around this problem.
Beforehand, what specific device are you currently using? Are you using an Android or an iOS? Additional details can help me get on the same page.
In the meantime, I've got some troubleshooting steps for you. These are:
Ensuring that your printer has ink and is working.