Step 1: Create an Adalo Account and Start a New Project

• Go to the Adalo website and sign up for an account if you haven't already.
• Once logged in, click on "Create New App".
• Choose the platform (native mobile or web), and select a blank template to start.

Step 2: Set Up Your Screens

• Create Login and Registration screens if they aren't there already.
• You'll need a screen for entering the phone number, another screen for entering the verification code, and a final screen to show the successful verification.

Step 3: Configure the User Database

• Navigate to the Database section.
• Add a "PhoneNumber" property to the Users collection to store the user's phone number.
• Add a "VerificationCode" property to store the code sent via SMS.

Step 4: Integrate an External SMS Service

• Choose a third-party SMS service like Twilio or Nexmo.
• Sign up for an account and get your API key and credentials.
• In Adalo, go to the Settings tab and then to External Collections.
• Set up an external collection to send the verification code via the SMS API.

Step 5: Design the Phone Number Input Screen

• Drag and drop an input field for the phone number onto the screen.
• Ensure that this input field is set to update the "PhoneNumber" property in the Users collection.
• Add a button that will trigger the SMS sending action.
• Configure this button to generate a random verification code and update the "VerificationCode" property. Then use the external SMS collection to send this code to the user's phone number.

Step 6: Design the Verification Code Input Screen

• Drag and drop an input field for the verification code onto the screen.
• Add another button that will trigger the verification action.
• Configure the button to compare the inputted verification code with the "VerificationCode" property in the Users collection.
• If the codes match, navigate the user to the success screen. If not, display an error message.

Step 7: Test Your Application

• Preview your app using Adalo's preview feature.
• Go through the entire verification process to ensure it works correctly, from entering the phone number to receiving and verifying the SMS code.

Step 8: Go Live

• Once everything is tested and working, publish your app to the desired platform (web, iOS, or Android).
• Make sure you have enough SMS credits in your third-party service account to handle user verifications.