REST API is not yet supported for this mailbox

[SubbaReddi]

Hi Team, I see bookaroom app is not working(When user clicks on "More rooms", task module opens and time zone dropdown is empty) for the accounts in one of the customer tenant. When i check the logs, see the following exception: "REST API is not yet supported for this mailbox"

User accounts is not having exchange online license. My understanding is this app template was targeted for exchange online and will not work for onprim. If exchange online license is mandatory, Can you update the documentation to refer the same?