Invoice requirements: serially numbered documents with prescribed details and digital-authenticated records to support service tax compliance. Service tax compliance requires maintenance of records (including electronic records authenticated by digital signature under Board conditions) retained for five years; issuance of serially numbered invoices, bills or challans within prescribed timeframes containing provider and recipient details, description and value of service, and service tax payable, with tailored rules for banking, passenger transport, goods transport agencies and ISDs; and maintenance of specified detailed registers for cenvat credit for input/capital goods and input services.