Was the incorrect cash applied to an invoice? Or posted as unapplied cash?
As long as the cash (and invoice(s)) for the wrong customer have not been cleared to History, create a new Cash batch entry for the wrong customer, and enter a negative payment amount (equal to the positive amount from the bad payment). Ensure that the Show All checkbox is selected, and then the wrong cash and applied invoice(s) will be displayed on the detail grid. Apply the negative cash to all the same invoices, and that will reverse the effects of the wrong cash. Then create a second cash entry to the correct customer.
If the cash entry was unapplied, follow the same steps as above but apply to the 'unapplied cash' instead of paid invoices. Then do a second entry to the correct customer.
All accounting will correctly be reversed for the incorrect cash payment.
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Regards,
Softrak Tech Support