Microsoft announced in October 2022 that Azure compute Reservations purchased on or after 1 January, 2024 would no longer be able to be exchanged. Then, in October 2023, they announced that there would be a grace period giving customers until at least 1 July, 2024 to exchange their Reservations for Azure Dedicated Host, Azure App Services, and Reserved Instances. The latest announcement in May 2024 states that the grace period is now extended until further notice.

Find the announcement here: https://bit.ly/4bPH4gl, and a useful article with some example scenarios here: https://bit.ly/3MdGC0m.