Some of the reasons why the balance sheet and GST summary may not match in BUSY are:
1. The tax account selected in the sale/purchase type and tax bill sundries is incorrect.
2. The tax type selected in the tax accounts, such as IGST, CGST, SGST, etc., is wrong.
3. The accounting configurations in the bill sundry for other charges and discount are not as per your requirements.
4. The GST nature selected in the accounting vouchers is wrong.
5. The ITC eligibility selected in the purchase or accounting vouchers is improper.
There may be other reasons depending on the situation.