Extension Field as Key Figure

Hi expersts,

I added an extension field availability with list values available, booked and sold to Product object and Product Master Data data source. Now I want to make a a heat map report by product availability (a mesh report common for appartment sellers).

How can I use availability extension field as a key figure?

I tried to create a restricted key figure based on counter with fixed restriction by value of availability, but it is not possible to add it. Here are screenshots:

- before I aded fixed value

- adding a value

- after adding a value

Best regards,

Nadezhda Rukavishnikova