How to pass array parameter to stored procedure in my case without changing C# code?

I have to pass the multivalue parameter to a stored procedure. The datatype which is passing from C# code is string[].

This is my stored procedure

CREATE PROCEDURE spRecords
    @Department VARCHAR(MAX) = NULL
AS
BEGIN
    SELECT
        ItemDetails,
        Total,
        Department
    FROM
        ItemRecords
    WHERE
        (Department.Name IN (@Department) OR @Department IS NULL)
END

I get the following error message

Cannot convert from string[] to string

I saw this stack overflow second answer to declare variable like @INFO_ARRAY ARRAY nvarchar(max). But I don't know how I should apply that in my case

Update

I don't want to change any code from C#. I am using one tool that will directly pass string[] array parameter like datasource