Thanks for connecting with us in the Community. Let me share some insights about adding a vendor.
In QuickBooks Online (QBO), the feature to automatically add an account to vendor transactions is currently unavailable on the VendorInformation page. As a workaround, you can associate a product or item to your preferred vendor.
Click on the Gear icon and choose Products and Services.
Choose Inventory, Non-inventory, or Service.
Enter some necessary information.
Choose a vendor in the Preferred Vendor drop down.
Click on Save and close.
I've attached some screenshots, so you'll know what I'm referring to.