The customer asked me to cancel one of his orders and transfer funds from the first order to the second. How can I do this?

Open the order you want to cancel. Cancel it. See how to change order statuses here. On the Payments tab, view the payment amount. Copy the order number.
Now open the order where you want to transfer money to.
Open the Manage tab.
Set the Take payment checkbox and enter the amount of the payment.
Specify a payment type — Using another order funds.
Insert the canceled order number.
Click Process.
After that, the balance changed. And the Payments tab displays information about this transaction.
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