Microsoft announced in October 2022 that Azure compute Reservations purchased on or after 1 January, 2024 would no longer be able to be exchanged. There is now a grace period meaning that customers have at least until 1 July, 2024 to exchange their Reservations for Azure Dedicated Host, Azure App Services, and Reserved Instances. This is a useful article with some example scenarios: https://bit.ly/3MdGC0m.