When choosing a new payment method, all previous transactions are cancelled (except for the ones that are already cancelled). To support partial payment, for example when using a balance payment system, only payment that are not yet paid, i.e. transactions with a partially paid status, should be cancelled. The already paid amount should also be deducted from the transaction for the newly chosen payment method.
Summary
When choosing a new payment method, all previous transactions are cancelled (except for the ones that are already cancelled). To support partial payment, for example when using a balance payment system, only payment that are not yet paid, i.e. transactions with a partially paid status, should be cancelled. The already paid amount should also be deducted from the transaction for the newly chosen payment method.