Input parameter using a scalar UDF

I am trying to use a scalar UDF in an input parameter. I can use a stored procedure but when I try to find the function, it doesn't come up. As you see below, the function is available and I can use it in a normal Select statement. But when I try to find the function in the Input Parameter definition, it comes up 'No results found'. Is there anything I need to specifically to make it available? I copied the function code below.

CREATE FUNCTION ZFCC.Z_FISCAL_MONTH (ip_yyyymm_from nvarchar(6))
RETURNS ip_yyyymmm_from nvarchar(7)
LANGUAGE SQLSCRIPT 
SQL SECURITY INVOKER AS
BEGIN


ip_yyyymmm_from := left(:ip_yyyymm_from,4) || '0' || right(:ip_yyyymm_from,2);



END;