How do I record negative Vendor bill?
If it’s for vendor’s (or supplier’s) credit bill:

• Click Create “+” sign in the middle (see attached screenshot below for reference)
• Select “Vendor Credit” under Vendors
• It will leave credit balance on Accounts Payable under Vendor’s Name.

New QuickBooks Online Plus – How to enter various expenses in new QBO?

QuickBooks Online (QBO) Tutorial – Customer Invoice, Sales Receipt, Receive Payment, Bank Deposit