In each of the following situations, state at which date(s), if any, revenue will be recognised. Explain your reasoning.

A contract for the sale of goods is entered into on 1 May 2023. The goods are delivered to the buyer for one month's evaluation on 15 May 2023. If the buyer is happy with the goods the contract provides for further sales each month. The buyer pays for the evaluation goods on 3 May 2023. The evaluation goods are returnable under normal warranty conditions until 30 June 2023.