I'm here to make sure you're able to turn on the CIS feature in QuickBooks Online (QBO), @Edwardo80.

You'll first have to select the Account and settings option after pressing the Gear icon. From there, you'll find the Advanced menu to get you through the Enable CIS bit. This will let QuickBooks calculate your CIS deductions, track CIS withheld or suffered, and create reports for HMRC.

I've attached screenshots below for your reference.

Once you're done, you're now set to add contractors and subcontractors to start processing CIS transactions. Then, make sure to record payments you make, as well as those you receive from them. Here's a guide on how to create invoices and bills with CIS on.

Also, to further guide you in using the CIS feature in QBO, I'd recommend checking out our help articles to get you off the ground: CIS guide in QuickBooks Online.

Please don't hesitate to let me know in the comments if you have other taxes and CIS concerns and questions about managing your transactions in QBO. I'll gladly help. Take care, and I wish you continued success, @Edwardo80.