I have "Liability" account in Gnucash for my credit card. Each expense made using my card is shown there as "Charge", while each payment I made to the credit card account from my checking account is shown as "Payment". I want to calculate the sum of all charges on the card to work out the expected cashback from the credit card provider. How do I do that?
Reports -> Income & Expense -> Cash Flow
Options -> Set Start Date/End Date to match billing cycle -> Accounts -> Clear All -> Select Credit Card only -> Money Out
To adjust Refund and Chargeback, you need to cancel out with Money In items except Bank.