Hi Naadira,

Header level remaining shows the balance to be settled in the Mixed Payment. In other words it shows the balance to be paid or received. It will only be zero if you are making a offset transaction using mixed payment.

If it is payment, it is only enough matching transactions level remaining amount zero which means header level payment amount is completely matched with a invoice.

Hope this will help.

Regards,

Akila

Hello,

In Mixed Payment on General tab there are fields Opening Balances and Closing Balances. 

Remaining amount field in the header of Transactions tab shows result of the formula: Closing Balance minus Opening Balance minus total of mixed payment transactions - it is the difference remaining to be registered as mixed payment transaction(s).

To make the difference zero, total of mixed payment transactions must be the difference between opening and closing balance of payment.
If both opening and closing balance is null, mixed payment can be approved/posted even if the remaining amount is not zero.