Count rows from related table (M2M)

Hi pawelk3 ,

It seems that what you are trying to create is a measure, please update the formula of measure[Conversions] as below. Later check if it can return your expected result...

Conversions =
VAR _seldate =
    SELECTEDVALUE ( Lead[CreatedOn] )
RETURN
    CALCULATE (
        COUNT ( Contact[ContactId] ),
        FILTER (
            Contact,
            Contact[ContractDate] >= _seldate
                && Contact[ContractDate] <= _seldate + 90
        )
    )

In addition, you can review the following blog to know the common DAX errors...

DAX error messages in Power BI

If the above one can't help you, please provide some raw data in your table (exclude sensitive data) with Text format, your treemap Fields settings and your expected result with backend logic and special examples? It would be helpful to find out the solution. You can refer the following links to share the required info:

How to provide sample data in the Power BI Forum

How to Get Your Question Answered Quickly

And It is better if you can share a simplified pbix file. You can refer the following link to upload the file to the community. Thank you.

How to upload PBI in Community

Best Regards