Thank you for posting in the Community. Allow me to help share some insight about creating an invoice in QuickBooks Online.
Are you trying to create invoice according to customer name, invoice number or by the due date, etc. in QuickBooks? If so, that option isn't available. You need to create invoice manually or create recurring transactions for customers you invoice regularly.
However, if you're trying to sync CRM transactions (invoices) in order to QuickBooks, I recommend reaching out to the third party app's Customer Support for further assistance. They can check the connection set up between your CRM account and QBO and help you get back on track.
Here's how to contact CRM:
On the left pane, click Apps.
Choose the My Apps tab, select your CRM app.
Under the Overview tab, you'll see their contact information.
I've also added a link which contains videos and webinars about QuickBooks Online for future reference: QuickBooks Tutorials.
That should point you in the right direction today. Please know that I'm just a post away if you have any other questions about creating an invoice in QuickBooks. I'll be happy to help you out. Have a great day ahead.