Variables syntax error message

Hello, I'm trying to use variables within my measure / DAX expression however I'm getting the below error message for the below DAX expression.

Error Message: The report measure MeasureName has a syntax or semantic error at line 2, position 5, reported by Analysis Services: 'The syntax for PerformanceIndexMTD' is incorrect.'.

We're on SSAS 2014... and we have a live connection to the data model on SSAS 2014.  Could this be the issue since I'm reading that variables only became available in SSAS 2015?

It's confusing because some other articles read as if it's the tool that you're working on needs to either be Power BI or Excel 2016 for variables to work. https://www.sqlbi.com/blog/marco/2017/09/12/the-easiest-way-to-start-using-variables-in-dax/

Anyone have a clue as to what my problem is?

Perf - Relative - MTD 2 (Variables) = 
VAR PerformanceIndexMTD =
    CALCULATE ( SUM ( Performance[MTD] ), Performance[Account Type] = "Index" )
VAR PerformanceAccountMTD =
    CALCULATE (
        SUM ( Performance[MTD] ),
        Performance[Account Type] = "Account",
        Performance[IndexNo] = BLANK ()
    )
VAR PerformanceRelativeMTD = PerformanceAccountMTD - PerformanceIndexMTD
RETURN
    PerformanceRelativeMTD