How validation works in Reply sequences
Automated SMS steps in sequences include built-in phone number validation. Before sending a message, the system checks the contact’s phone number and determines whether it is valid and what type of number it is. After validation, SMS messages are sent only to numbers that can receive them. This helps avoid delivery errors and keeps your SMS statistics accurate.
Why is phone number validation important?
Some SMS messages cannot be delivered because:
The phone number is incorrect or does not exist
The number is a landline and cannot receive SMS
Without validation, the system may still attempt to send messages in these cases. This can lead to failed deliveries and unclear reporting.
Validation helps ensure that messages are sent only to reachable recipients.
How to use phone number validation
Phone number validation works automatically in Auto SMS steps. No manual setup is required. Here is how it works:
Add an Auto SMS step to your sequence
The system automatically checks each contact’s phone number
Based on the result, the system decides whether to send the SMS
We use the Twilio Lookup API to check all the phone numbers linked to the contact profiles. After validation, the system receives the types of phone numbers and then processes those phone numbers according to their types.
Possible results of the validation are valid, invalid, and unknown. Here's a full overview of how it works:
Status of phone numbers | Description | Action with auto SMS |
Valid (mobile-compatible numbers) | The entered phone number is correct.
As mobile phone number type, a system recognizes mobile, fixed VoIP, non-fixed VoIP, personal, tollFree, premium, shared-cost, uan, or pager phone numbers. | Auto SMS will be sent. After the validation, the Call button will be active.
 |
Valid + phone number type is Landline | The entered phone number is correct, but messages cannot be sent to it.
As a landline phone number type, a system recognizes landline and voicemail. | Auto SMS will not be sent. The status of contact in the sequence is Missing data. An icon of a house will be shown near a contact's number.  |
Invalid | The phone number is missing or has been entered incorrectly. | The phone number is missing or incorrect. An invalid number icon appears next to the number.  |
Unknown | The phone number is entered correctly, but we cannot check whether it is a mobile or landline number due to a lack of information from the carrier. | We send SMS anyway. |
Managing phone numbers
Each phone number is validated once, and the result is stored. If you edit a contact’s phone number, it will be validated again automatically.
💡Limitations and important notes
Validation is required for Auto SMS steps and cannot be disabled.
Phone numbers from Canada are not fully supported. Validation may not work due to legal restrictions, and SMS delivery is not guaranteed.
Validation is charged per request. Each phone number check costs $0.008 and is deducted from your wallet. This price is determined by Twilio's pricing (Line Type Intelligence tariff).
Validation is processed automatically for all contacts with phone numbers in sequences.