Free/Busy only works with Microsoft EWS component and Gmail accounts.
If the free/busy endpoints return empty arrays, i.e. no results then the reason is typically that the provider is not returning any values. This is especially an issue with Microsoft accounts.
- Have the customer run EWS test, does the (Getting user availability and confirming results against expected values) part of the test pass?
- If it is failing then please look pass the following information on the mai administrator: