MainActivity.java

mSend.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        try {
            post(mContext.getString("YOUR_NGROK_URL/sms"), new  Callback(){

                @Override
                public void onFailure(Call call, IOException e) {
                    e.printStackTrace();
                }

                @Override
                public void onResponse(Call call, Response response) throws IOException {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            mTo.setText("");
                            mBody.setText("");
                            Toast.makeText(getApplicationContext(),"SMS Sent!",Toast.LENGTH_SHORT).show();
                        }
                    });
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
});