Timing of Cenvat credit: invoice receipt and payment conditions determine entitlement and reversal obligations under the Rules. Input service under the Cenvat Credit Rules covers services used by providers of output services or manufacturers in relation to manufacture and clearance, includes a non exhaustive list of business services, and specifies exclusions for certain construction, motor vehicle renting and personal employee services. Rule 4 permits credit on receipt of the invoice and requires reversal where payment and tax on the input service are not made within the prescribed period or where refunds/credit notes are received; special spreading and allowance rules apply to upfront charges for assignment of rights to use natural resources.