There are only a few possibile cases when you might get a difference in the opening balance.
This can either be due to wrong entry of data at the time of migration or double entry of items or probably you are referring to a post/pre dated entry while comparing the opening balance.
Let’s consider an example to understand this scenario better.
If you have entered an amount for AR in Opening Balance and you also need to import / create invoices (invoice date should be before the opening balance date) for the amount you entered in the Opening Balance for AR, you will end-up in double counting. In this case, you will be getting a difference in the closing balance of the previous software and the opening balance in Zoho Books.
and GST filing.