On Response Code 400 I cant get data retrofit

Question

private void getotp(String name,String phone, String dob){
        btnVerify.setClickable(false);
        dialog.show();
        //Toast.makeText(BookToken.this,blockname,Toast.LENGTH_LONG).show();
        Retrofit retrofit = RetrofitClient.getRetrofitInstance();
        apiInterface api = retrofit.create(apiInterface.class);
        Call<otp> call = api.SendOtp("covishield",dose,age, blockname, location, phone);
        call.enqueue(new Callback<otp>() {
                         @Override
                         public void onResponse(Call<otp> call, Response<otp> response) {
                             if (response.code() == 200) {
                                otp resp = response.body();
                                String Success = resp.getSuccess();
                             
                         
                                 dialog.cancel();

   if (response.code() == 200) {
otp resp = response.body();
                                String msg= resp.getMessage();
                                 dialog.cancel();
                                 btnVerify.setClickable(true);
}
                             }else {
                                
                                 dialog.cancel();
                                 btnVerify.setClickable(true);
                               
                             }

                         }



            @Override
            public void onFailure(Call<otp> call, Throwable t) {

                Toasty.error(BookToken.this, "SomeThing Went Wrong", Toast.LENGTH_SHORT, true).show();

                dialog.cancel();
                
            }
        });
    }

here on response code 400 api echo json data on value message, but on my mnethod i can get the message if i try to get message it will we force close due to null object refer, its retrofit or httpintercepter error? please let me know this