Waterfall: Carrier Filtering: Phone Numbers in SMS Message Body

Overview

Wireless carriers may silently filter (block) outbound SMS messages that contain phone numbers in the message body. This can cause campaign flows to appear broken — messages are not delivered, consumers receive no response, and the campaign sequence stalls — even though the platform itself is functioning correctly.

Symptoms

• A message in the middle of a campaign flow is not delivered after the consumer replies.
• The consumer must send an additional unprompted message to trigger the next step.
• When the flow does resume, it may fire an error such as "please send a valid 10-digit phone number" instead of the expected message.
• The issue is isolated to a specific message step; earlier and later messages in the flow work normally.
• No platform-side errors or delivery failures are visible in the dashboard.

Root Cause

Wireless carriers use automated content filtering to flag messages that look like spam or phishing. Messages that include a phone number in the body — even as an example or instruction — are frequently caught by these filters and silently dropped before reaching the recipient.

Example of problematic message copy: "Thanks! Please send us your phone number on your Venmo account. Reply w/ your 10-digit phone number (example 4155555151)."

Resolution

Remove any phone number — including example numbers — from the message body. Replace the affected message copy with a version that instructs the consumer to reply without providing a numeric example.

Steps to Resolve

1. Identify the message step in the campaign where delivery is stalling.
2. Open the message copy for that step.
3. Locate any phone number or numeric example (e.g., "example 4155555151") within the body.
4. Remove the example phone number entirely from the message copy.
5. Save the updated message.
6. Monitor delivery on the next consumer interaction to confirm the message is now being sent.

Best Practices for SMS Message Copy

• Never include phone numbers — real or example — in the SMS message body.
• Avoid other content patterns commonly flagged by carriers, such as URLs shortened with generic services, dollar amounts combined with action verbs, and repeated special characters.
• After updating message copy, always test the full flow end-to-end before returning to production.
• If delivery issues persist after removing phone numbers, review the full message copy for other carrier-filter triggers and contact Support.

Still experiencing issues after following these steps? Contact the Support team and reference this article for faster triage.