DAX Measure error on concentrate, within Concentrate

Hi Experts

Cannot see where the error in in the following when applying it to managed role.

the end result need to be (country)[Bu_Code]

VAR _User = CONTAINSSTRING(
    USERPRINCIPALNAME(),
CONCATENATE(   
CONCATENATE(
        "(",
        CONCATENATE(
            [country_dim.country_name],
            ")"),
                CONCATENATE(
                    "["
                     CONCATENATE(
            [bu_code],
            "]")
    )
)
)
RETURN