Creating a drill-through button destination conditionally

Hi 🙂 

I'm following the microsoft page: https://docs.microsoft.com/en-us/power-bi/create-reports/desktop-drill-through-buttons#set-the-drill-through-destination-conditionally trying to configure a drill through button that will just display/go to the drill through based on a condition. I have this column 'Amended' which takes a boolean True (1) and False (0). I've written a DAX Measure as recommended in the post to feedback the drill through location based on the condition I would like: 

AmendmentsDrillThrough = If(SELECTEDVALUE('fact Orders'[IsAmended])== 0, " ", "Amendments")

Following the post, it suggests next i just need to go into Action in my button and add it as a conditional formatting destination. I click the fx and go to add this measure, and it wont let me select it - it's greyed out. Any ideas? 

I'm assuming it's because its not a Text value? 

But again this doesn't seem to be something i can change: 

Any ideas?