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Why didn't my SMS get delivered? Troubleshooting SMS delivery issues

A troubleshooting guide for SMS delivery issues in Spark, covering log statuses, common failure reasons, opt-in verification, compliance checks, automation troubleshooting, and when to contact support.

Written by David Spark

Why didn't my SMS get delivered? Troubleshooting SMS delivery issues

If a message shows as sent but your member never received it, there are several possible causes. This guide walks you through how to diagnose and resolve the most common SMS delivery issues in Spark.

Section 1 — How to read the SMS log

The SMS log records every message sent from your account. To access it, go to Left Side Menu Bar > Communication Center > SMS Logs. There are also SMS logs available on a client by client basis in their profile, in the SMS Messages tab.

Each message will show one of the following statuses:

  • Waiting — The message has been created and is queued to be sent. It has not left Spark yet. In this stage, an SMS message can be cancelled.

  • Sent — The message has left Spark and been handed off to the carrier to be delivered.

  • Failed — The message could not be delivered. See the sections below for common reasons why.

  • Cancelled — If you cancel a message while it's in the Waiting stage from the contact's profile, this will be the status shown.

Note: A status of "Sent" is not the same as "Delivered." If your member says they didn't receive a message that shows as Sent, continue through the steps below.

Section 2 — Common reasons a message doesn't reach the recipient

Even when a message shows as Sent, delivery can fail for several reasons:

  • Carrier filtering / blacklist rule — Mobile carriers may filter messages that appear spammy, contain certain content, or come from numbers not fully registered. This doesn't always result in a complete block — some messages may go through while others don't, which is why you might see delivery working inconsistently to the same number. If you see the error: "The message From/To pair violates a blacklist rule" — this is the likely cause. Contact Spark support to review your sending number and message content.

  • Recipient has opted out or was opted out on their profile — If the contact previously replied STOP, they are opted out at the carrier level. This applies to the phone number itself, not just the contact record. This means if multiple contacts in Spark share the same phone number, messages to all of them will fail at the carrier level with the error: "Attempt to send to unsubscribed recipient (21610)". However, the SMS Subscribed checkbox will only appear unchecked on the contact that was originally messaged. The other contact sharing the same number may still show as subscribed in their profile, even though their messages will also fail. See the Managing SMS opt-outs article for next steps.

  • Number marked invalid — The phone number on file may be incorrect, disconnected, or not capable of receiving SMS (e.g. a landline).

  • Sender number not fully approved — If your Spark SMS number has not completed all three compliance phases, outbound messages may be filtered or blocked entirely. See Section 4 below.

  • Message delivered to spam/junk — Some carriers or devices may route messages to a spam or junk folder rather than the main inbox, even when the message shows as Sent. Ask the recipient to check their spam folder on their messaging app and, if possible, mark your number as a trusted contact to prevent future filtering.

Section 3 — How to confirm a recipient is opted in

There are two ways to check whether a contact is opted in to receive SMS:

Option 1 — Check via the contact's profile (recommended for checking one contact)

  1. Go to the contact's profile.

  2. Click Edit Contact.

  3. Scroll down to the SMS Subscribed checkbox. If it is unchecked, the contact is not opted in and will not receive SMS messages.

Important: The SMS Subscribed checkbox only reflects the status of the contact you are viewing. If another contact in Spark shares the same phone number and that contact opted out by using the "STOP" reply, this checkbox may still appear checked — even though messages will fail at the carrier level. If you are seeing the "Attempt to send to unsubscribed recipient" error, check whether any other contact in your system shares the same phone number.

Option 2 — Check via the Unsubscribers list (for a broader view)

  1. Go to Left Side Menu Bar > Communication Center > SMS Logs & Templates > SMS Unsubscribers.

  2. This section lists all contacts who have unsubscribed. You can scan the list to see if a specific contact appears here, though it is easier to use Option 1 when checking a single contact.

Section 4 — How to confirm your sending number is fully approved

Your Spark SMS number goes through four compliance stages. You can check your current stage in your SMS settings under compliance information. Here is what each stage means:

  • 0 out of 3 — Nothing has been submitted yet. Compliance setup has not been started.

  • 1 out of 3 — Your brand has been submitted to Twilio. Submission is in progress.

  • 2 out of 3 — Your brand has been accepted and your campaign has been started. Awaiting final approval.

  • 3 out of 3 — Fully compliant. Your number is approved and ready to send messages reliably.

If your number is below 3 out of 3, messages may be filtered or blocked by carriers. Do not rely on SMS for critical communications until you reach 3 out of 3.

To check your compliance status, go to Left Side Menu Bar > Settings > SMS > SMS Phone Number.

For full compliance setup instructions, see the SMS Compliance article.

Section 5 — My automation fired but no SMS went out

If an automation step triggered but no message was sent, check the following:

  • Confirm you have enough SMS Creditst available on your account. These are viewable at the top right of your Dashboard.

  • Confirm the contact's phone number is valid and they are opted in (see Section 3).

  • Check the SMS log to see if a message appears at all — if it shows as Failed, note any error details.

  • Verify the sending number has completed all compliance phases (see Section 4).

Section 6 — When to contact Spark Support

If you have worked through the steps above and messages are still not delivering, contact Spark support and include the following:

  • The name and phone number of the affected contact

  • The date and approximate time the message was sent

  • The status shown in the SMS log (Sent, Failed, etc.) and the exact error message if one appears

  • Whether the issue affects one contact or multiple contacts

  • Whether this started happening recently or has always been the case

  • A screenshot of the SMS log entry if possible

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