The opening balance entries for customers and vendors track to Uncategorized Income (customers) or Uncategorized Expense (vendors).
If the customer/vendor has an outstanding balance, before the start date :
Enter the outstanding balance in the respective AR/AP field with the start date.
Import unpaid invoice or bill for each customer and vendor. The unpaid transactions will result in open balances for customers and vendors, and those balances will result in A/R and A/P opening balances.
This option will be helpful if you need to keep track of individual sales or bills that make up your customer and vendor opening balances. However, you can also make use of the Reports module as well, to track individual sales by customer etc.
and GST filing.