Must declare the scalar variable @user

hello !

i have the following code:

private void setActivated(bool activationB, string user)
        {
            SqlConnection conn = new SqlConnection(GetConnectionString());


            string sql = "UPDATE NannyUsers SET activationB = @activationB WHERE username = @user";
            try
            {
                conn.Open();
                SqlCommand cmd = new SqlCommand(sql, conn);

                cmd.Parameters.Add("@activationB", SqlDbType.Bit).Value = activationB;
                

                cmd.CommandType = CommandType.Text;
                cmd.ExecuteNonQuery();
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                string msg = "Insert Error:";
                msg += ex.Message;
                throw new Exception(msg);
            }
            finally
            {
                conn.Close();
            }
        }

it returns the following error: 

Insert Error:Must declare the scalar variable "@user"

i cant understand why or how to fix it and i spent an entire hour serching for answears online... anny would be highly appreciated!