Hi, @abritojtf. 

I'll lay down a few steps to help you convert a sales order into an invoice in QuickBooks Online.

Please know that sales orders are available in QuickBooks Desktop. Thus, we can utilize estimates and turn them into an invoice. I'll show you how you can do it:

1. From the Sales menu, select All sales.
2. Find and open the estimate you want to convert.
3. Check the status of the estimate under the customer's name. You can only convert an estimate with an Accepted or Pending status. If that's the status, skip this step. If the status is Closed or Rejected, select the ▼ dropdown. Choose either the Accepted or Pending status, then select Save.
4. Click Create invoice.
5. Make any updates to the invoice if needed. 
6. If you're ready to send the invoice to your customer, select Save and send. Or choose Save and close if you want to send the invoice later.

I'll add this article for more insights about converting your estimate to an invoice: Convert an estimate into an invoice in QuickBooks Online.

Furthermore, this resource can help you if you want to personalize and add specific information to your sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm still ready to back you up if you need more help with invoices or estimates. I'll keep the thread open so you can comment back. Keep safe always, and happy holidays.