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.
| Before (blocked by carrier) | After (delivered successfully) |
|---|---|
| "Reply w/ your 10-digit phone number (example 4155555151)." | "Reply with your 10-digit phone number." |
Steps to Resolve
- Identify the message step in the campaign where delivery is stalling.
- Open the message copy for that step.
- Locate any phone number or numeric example (e.g., "example 4155555151") within the body.
- Remove the example phone number entirely from the message copy.
- Save the updated message.
- 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.