how to "count distinct" a field in a pivot table

Hi everyone,

the following article* states that the summary function count distinct only works when you https://support.office.com/en-us/article/create-a-data-model-in-excel-87e7a54c-87dc-488e-9410-5c75dbcb0f7b.

I think I've followed all the steps, described in the link/article but I still can't apply the count distinct function.

Any tips / advice would be much appreciated! 

*:

https://support.office.com/en-us/article/sum-values-in-a-pivottable-9ee73790-646a-42c9-9fc7-e1ca30096d9c?ui=en-US&rs=en-US&ad=US