Reconciliation of GSTR returns requires adjustment of tax and ITC based on auto-populated GSTR-1/GSTR-2 data and ledger debits. System-based reconciliation compares information in FORM GSTR-1 and FORM GSTR-2 with returns filed in FORM GSTR-3B: the portal auto-populates FORM GSTR-2A and drafts Part A of FORM GSTR-3. Taxpayers must amend GSTR-1/GSTR-2 invoice-level and other inward-supply details to correct liabilities and ITC. Where FORM GSTR-3 shows higher tax than paid in FORM GSTR-3B, additional tax must be paid by debiting the electronic cash or credit ledger with interest; excess ITC evidenced in FORM GSTR-2 is credited to the electronic credit ledger. Returns are valid only after payment and matching procedures are completed.