Related function not working

Anonymous 

The error "The column either doesn't exist or doesn't have a relationship to any table available in the current context" occurs because of the limitations of DirectQuery. Currently, a calculated column on an import table can refer to other tables, but a calculated column on a DirectQuery table can refer only to columns on the same table. So when you try to create a calculated column on the many-side DirectQuery table, it cannot relate to columns on the one-side table and you see the error.

Additionally, calculated columns on a DirectQuery table are limited to being intra-row, as in, they can only refer to values of other columns of the same table, without the use of any aggregate functions. Functions that aren't supported aren't listed in autocomplete when authoring the DAX for a calculated column, and would result in an error if used.

Reference:

https://docs.microsoft.com/en-us/power-bi/transform-model/desktop-composite-models#limitations-and-considerations

https://docs.microsoft.com/en-us/power-bi/connect-data/desktop-directquery-about#modeling-limitations