How to reference a value on related table

I am trying to write a measure (DSO_Measure) that I could reference a value (DaysInMonth) on dim table (Calendar) because there are relationships with other two Fact tables (AR_Aging & Transactions) to do a calculation.

 

This is a measure (DSO_Measure) I am trying to write to do a calculation:

I tried with as shown on the bottom, but it did not get the right calculation numbers. 

 

 

There is a relationship between two Fact tables (AR_Aging & Transactions) and Calendar (dim) table.

 

Bottom is an image for the dim table (Calendar).

I only captured the portion of image for February 2022 value (DaysinMonth), which is 28.

How do I express so that it could reference the right month?

For this case, it should only point to 28 for February 2022.

If it is January or December, it should reference 31 in the Calendar table.

If it is November or September, it should reference 30 in the Calendar table, etc..

 

Thanks.