Please am running the following codes and getting the error "Must declare the scalar variable "@Firstname"."

SqlCommand comm = new SqlCommand("INSERT INTO APPLICANTDETAILS(Username,Password,Firstname,Lastname,OtherNames,dateofbirth) VALUES(@Username,@Password,@Firstname,@LastName,@OtherNames,@dateOfbirth)", conn2);

comm.Parameters.Add("@Username", SqlDbType.VarChar, 100).Value = app.Username;
            comm.Parameters.Add("@Password", SqlDbType.VarChar, 100).Value = app.Password;
            comm.Parameters.Add("@Firstname", SqlDbType.VarChar, 100).Value = app.FirstName;
            comm.Parameters.Add("@LastName", SqlDbType.VarChar, 100).Value = app.LastName;
            comm.Parameters.Add("@OtherNames", SqlDbType.VarChar, 100).Value = app.OtherNames;
            comm.Parameters.Add("@dateOfBirth",SqlDbType.VarChar,50).Value = app.DateOfBirth;

try
            {
                comm.Connection.Open();
                comm.ExecuteNonQuery();
                
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                comm.Connection.Close();
            }