Two-way SMS communication has become a must-have feature for modern applications, enabling real-time, interactive messaging experiences. Whether it’s for sending OTPs, notifications, or enabling customer support, two-way SMS allows businesses to engage with users directly and effectively. Twilio, with its powerful and easy-to-use API, simplifies the process of integrating SMS functionality into your applications.

In my last project, implementing two-way SMS was a crucial requirement. However, I faced several challenges due to a lack of proper resources and scattered documentation. From handling incoming messages to managing responses dynamically, there were many roadblocks that required creative solutions.

In this blog, I’ll share a step-by-step guide on implementing two-way SMS in a Ruby on Rails application using Twilio. Along with practical code examples, I’ll also cover common challenges developers face and how to overcome them — so you don’t have to go through the same struggles I did!

One-Way SMS (Outbound Messaging)

This is used when businesses only need to send notifications, alerts, or marketing messages without expecting a response.

Examples:
Order Updates: “Your order #12345 has been shipped!”
Appointment Reminders: “Hi Raj, your appointment with Dr. Sharma is scheduled for tomorrow at 10 AM.”
Promotional Messages: “Limited-time offer! Get 20% off your next purchase. Use code: SAVE20.”

Setting Up Twilio SMS Service in Your Application

To integrate Twilio into your application, follow these steps:

Step 1: Set Up Twilio Account

Sign up for a free Twilio account.
Get a Twilio phone number that supports SMS.
Note down your Account SID, Auth Token, and Twilio Phone Number from the Twilio console.

Step 2: Install the Twilio Gem (for Ruby on Rails)

Add Twilio to your Gemfile and install it:



1. Configure Twilio Credentials
In config/initializers/twilio.rb, store your Twilio credentials securely:

Twilio.configure do |config|
  config.account_sid = ENV['TWILIO_ACCOUNT_SID']
  config.auth_token = ENV['TWILIO_AUTH_TOKEN']
  config.twilio_phone_number = ENV['TWILIO_PHONE_NUMBER]
end

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2. Create a Twilio SMS Service
# app/services/twilio_sms_service.rb

class TwilioSmsService
  def initialize(to, message)
    @to = to
    @message = message
    @from = ENV['TWILIO_PHONE_NUMBER'] # Twilio's registered phone number
  end

  def send_sms
    client = Twilio::REST::Client.new
    client.messages.create(
      from: @from,
      to: @to,
      body: @message
    )
  rescue Twilio::REST::TwilioError => e
    Rails.logger.error "Twilio Error: #{e.message}"
    false
  end
end

# app/controllers/sms_controller.rb
class SmsController < ApplicationController
  def send_sms
    phone_number = params[:phone_number] # User's phone number
    message = params[:message] || "Hello from our app!"

    sms_service = TwilioSmsService.new(phone_number, message)
    if sms_service.send_sms
      render json: { status: "SMS sent successfully" }, status: :ok
    else
      render json: { error: "Failed to send SMS" }, status: :unprocessable_entity
    end
  end
end

Two-Way SMS (Interactive Messaging)

Twilio 2-Way SMS allows businesses to send messages and receive responses dynamically, enabling real-time customer engagement.

Examples:
Appointment Confirmations: “Reply 1 to confirm, 2 to reschedule.”
Customer Support: “Reply with your issue, and our agent will assist you.”
Event Attendance: “Will you be attending the seminar? Reply YES or NO.”

How 2-Way SMS Works ?

1. User Receives an SMS About a Special Event — A business sends an SMS to a user about an upcoming event, a survey, or a special offer.

2. User Responds with Input — If the business needs user input (e.g., confirmation, feedback, or other responses), the user replies to the SMS with a specific keyword or message.

3. Twilio Captures the Input — Twilio processes the message and forwards it to your system.

4. Your System Handles the Data — Based on the user’s response, your application performs necessary database operations, such as updating confirmation status, storing feedback, or confirming a booking.

5.Automated or Manual Response is Sent — The system may send an automated response (e.g., “Thank you for confirming your attendance!”) or forward the message to a support agent for follow-up.

Step 1: Implement SMS Sending

Here’s a simplified service class to send SMS using Twilio in a Ruby on Rails application:

# frozen_string_literal: true

require 'twilio-ruby'

class TwilioSmsService
  def initialize
    @client = Twilio::REST::Client.new(ENV['TWILIO_ACCOUNT_SID'], ENV['TWILIO_AUTH_TOKEN'])
  end

  def send_sms(to, body)
    @client.messages.create(
      from: ENV['TWILIO_PHONE_NUMBER'],
      to: to,
      body: body
    )
    { success: true }
  rescue Twilio::REST::TwilioError => e
    { success: false, error: e.message }
  end
end

# How to Use It
#  Call the send_sms method wherever you need to send an SMS:

sms_service = TwilioSmsService.new
response = sms_service.send_sms('+919876543210', 'Hello! Your appointment is scheduled for tomorrow at 10 AM.')

Step 2: Set Up Webhook to Receive SMS Responses

A webhook is an endpoint that Twilio calls when an SMS is received. To process incoming messages, follow these steps:

Step 2.1: Create a Webhook Endpoint

Your webhook will listen for incoming messages and respond accordingly. In a Ruby on Rails application, you can set up a controller to handle Twilio’s webhook requests.

Now, define the webhook method inside controller

class SmsController < ApplicationController
  skip_before_action :verify_authenticity_token  # Required for handling Twilio's POST requests

  def receive_sms
    sender_number = params['From']
    message_body = params['Body'].strip.downcase

    response_message =
      case message_body
      when '1'
        "Thank you! Your appointment has been confirmed."
        # Perform your database related changes and actions.
      when '2'
        "Your appointment has been canceled. Let us know if you’d like to reschedule."
        # Perform your database related changes and actions.
      else
        "Sorry, we didn't understand that. Please reply with 1 to confirm or 2 to cancel."
      end

    twiml = Twilio::TwiML::MessagingResponse.new do |r|
      r.message(body: response_message)
    end

    render xml: twiml.to_s
  end
end

Step 2.2: Define Routes for Webhook

post '/sms', to: 'sms#receive_sms'

Step 2.3: Link Your Webhook in Twilio

1️⃣ Log in to Twilio Console

Go to Twilio Console.

2️⃣ Navigate to Your Phone Number

In the left sidebar, click on Phone Numbers → Manage Numbers.
Click on the Twilio phone number you are using for SMS.

3️⃣ Configure Messaging Webhook

Scroll down to the Messaging section.
Find the option “A Message Comes In”.
Select Webhook from the dropdown.
Enter your publicly accessible webhook URL:

Example:

https://your-app-name.com/sms/receive

Select HTTP POST as the method.

4️⃣ Save the Configuration

Click Save at the bottom of the page.

5️⃣ Test the Webhook

Send an SMS to your Twilio phone number from any mobile device.
Twilio should forward the message to your Rails webhook.
Check your Rails server logs to verify the incoming request.

Step 3: Verify Twilio Webhook is Working

To confirm everything is set up correctly:

Send a test SMS to your Twilio number (e.g., “1” to confirm).
Check your Rails logs to see if the webhook receives the request:
Twilio should respond with the expected message (e.g., “Thank you! Your appointment is confirmed.”).