GST payment obligations require supplier liability, reverse charge, TDS/TCS and electronic ledgers for timely compliance. Payment of GST is primarily the supplier's obligation, with exceptions under the reverse charge mechanism, e commerce operator liability, and government TDS/TCS requirements; the common portal computes tax based on outward supply declarations. Time of supply rules determine when liability arises, usually the earliest of receipt of payment, invoice issuance, or completion of supply. Taxpayers use electronically maintained E liability, E cash and E credit ledgers on the GSTN dashboard and must pay via electronically generated challans, supporting online payment, electronic reconciliation, and paperless accounting.