My Liability Tax Payable Account Show Negative Balance

When I purchase Inventory Items for resale, I have to pay 6% purchase tax for every single item.
I have created custom sale tax code and apply to the purchase invoice.

After I finished input the data, My Liability Tax Payable Account Show Negative Balance.

Any help how to fix this?

The negative balance is absolutely correct. Since you purchased an item and paid tax you have a negative balance until you make a sale which will be calculated against the current tax balance. As long as your purchases are higher than the sales you will have a negative Tax balance, meaning the Receiver owes you money.