Convert to MDX

Hi,

I have tried all kinds of iterations to convert this BSO calc to MDX. Any ideas/help? The Subvar &Prior_Year_1 is set to 'FY23'. I need it to return numeric value of '23'.

CalcMgrDoubleFromString(@substring(@name(&Prior_Year_1), 2))

This works: ((STRTONUM(SUBSTRING("FY23", 3, 4))))

However, substituting &Prior_Year_1 like: ((STRTONUM(SUBSTRING([&Prior_Year_1 ], 3, 4))))

Throws an error: Syntax error in input MDX query on line 10 at token ','

Also, can get it working on a Attribute, but in this instance Attribute will not work. Attribute method like this works:

(STRTONUM(SUBSTRING([Sites].CurrentMember.Vintage, 4, 6)) - 1)

Thanks. Appreciate any guidance.