What is the date of supply of a continuous supply of goods or services made after January 1, 2018?

Supply under contract: If a continuous supply is made under a contract and the recipient pays for the supply in instalments, then there is a special transitional rule permitting the seller to split the VAT accounting over the duration of the contract. Each instalment will be treated as a separate supply, with its date of supply as either the date on which the instalment falls due, or the date of payment (whichever occurs first). 

Supply without contract: Goods and services supplied on a continuous basis without a contract are treated differently. Each supply made with respect to an invoice or payment is considered a separate entity.