GSTR 3B reporting: consolidated monthly obligations for outward/inward supplies, ITC computation, ECO reporting and payment reconciliation. Form GSTR 3B requires monthly summary reporting of outward and inward supplies including categories for zero rated, exempt and reverse charge supplies, special reporting for supplies through Electronic Commerce Operators, and place wise reporting for inter State supplies to unregistered persons, composition taxpayers and UIN holders; it prescribes categorized ITC reporting with specified reversals and net ITC computation, and sets out payment, adjustment and verification obligations including use of ITC, cash payment, interest and late fee, with instructions on valuation, amendments and recent notification driven layout changes.