(1) Try “Vendor Credit” form (from create “+” sign > Vendor Credit under Vendors header) If you are using “Enter Bill” form to enter vendor bill and returning to the same vendor, you could use Vendor Credit form. It will show negative Vendor balance.
(2) For returning credit for Credit Card purchases > use Credit Card Credit form
(3) For returning credit for Debit Card purchases (or purchases paid by check) > use Make Deposits. In new QBO, they do not have Debit Card Credit or or Check Credit Expense Credit form at this time. There is a known problem using Make Deposits feature. It will not show up in the Vendors center. This is a huge known problem in new QuickBooks Online.