credit note concept

I received the sold goods back of taxable value ₹30000 the tax amount is ₹ 1500/- the buyer issue me Debit note and I gave him a Credit note, so I write the details of credit note in gstr1 in debit/credit note section , after refreshing it shows the tax liability of ₹1500/- how it is my liability, actually it is my credit
so ,IAM confused so please guide me .