During open invoice migration, if you encounter an error ‘Please select an A/R account for the invoice’,
check whether the customer has a default Receivables account selected.
For this go to the customer record and check on the Account information section under the Financial tab. Check whether a receivables account is selected.
If the field has the value ‘Use system Preference’ then navigate to setup>Accounting> Accounting preferences.
Under Accounts section of Items/Transactions tab, check whether a default receivables account is selected. If not choose the required one and save the changes.
Then perform the import again. The issue will now be resolved.