Token Comma Expected Error

You can always use Daxformatter.com to check your code.  In this case it comes back clean

a =
CALCULATE (
    VAR TotalSalePrice =
        CALCULATE (
            SUMX (
                'ODS_OWNER FACT_ORDER_LINE',
                IF (
                    'ODS_OWNER FACT_ORDER_LINE'[ORDER_LINE_FLG] = 1,
                    0,
                    'ODS_OWNER FACT_ORDER_LINE'[TOTAL_SALE_PRICE]
                )
            )
        )
    RETURN
        COALESCE ( TotalSalePrice, 0 )
)

but the outer CALCULATE() looks suspicious.  I don't think it is required.