Time of supply for continuous HAM highway services: invoice date or receipt of payment, whichever is earlier. Time of supply for HAM contracts, treated as continuous supply, is the invoice date or receipt of payment, whichever is earlier, when the invoice is issued on or before the contract-specified due date or completion event; if not, time of supply is the date of provision of service (which may be the due date of payment) or receipt of payment, whichever is earlier. Interest included in instalments/annuity is includible in the taxable value under section 15(2)(d) of the WBGST Act.