I have commercial tenants and I have to charge them for insurance for the building. It is not rental income, how do I invoice this and what category do I put it under.

Glad to have you here in the Community, @judy6.

In QuickBooks Online (QBO), we can set up commercial tenants as customers. I'll guide you how:

1. Go to the Sales menu, and then choose Customers.
2. Click the New customer tab.
3. Fill in the fields in the Customer information window.
4. Select Save.

Once done, create an account. I'd recommend seeking assistance with your accountant when setting up the account for further guidance about the posting accounts. Then, link it to a service item to track the insurance charge.

After that, create an invoice and then select the tenant and the service items in the appropriate fields.

For future reference, you can import multiple invoices at once so you'll be able to save time. 

I've also added this article about customizing invoices in QBO: Customise invoices, estimates, and sales receipts.

I'm always here if you need more help with your invoices and or anything else, by leaving a comment below. Have a wonderful day.