Hello there, D Lane.
Using sub-accounts for vendors is not yet available on the Online platform. Some features in QuickBooks Desktop are not available in QuickBooks Online. As a workaround, you can use account numbers similar to the vendor.
You can check this article for more information : Create subvendor names
If you need help setting up other things in QuickBooks Online, you can check our topics and articles here.
We always offer help whenever you need it. When you get back here, don't hesitate to leave a reply if you have other concerns about creating sub-vendor. You can also post a new thread for other QuickBooks Online questions.
