You probably know this issue, you have just paid 10€ and your friend will send you 5€. Now you have an expense that is higher than your actual part of the transaction. The solution here is to categorize the money you get from a friend in the same category as the expense. Then it will deduct your total expenses in that category. So if you spend 10€ and get 5€ from your friend, it will only look like you spent 5€.