Completion of service requires finalization of auxiliary activities before invoice issuance; invoice timing obligations apply to continuous services. The notice clarifies that for Service Tax Rules purposes an invoice must be issued within the statutory period after service completion, and completion includes all related activities that enable the provider to quantify and invoice the service (for example measurement or quality testing). The test of completion is the conclusion of those activities that place the provider in a position to issue the invoice; flimsy or irrelevant reasons cannot justify delay. This clarification also applies to determining completion dates in cases of continuous supply of service.