We paid three times to text a landline. Here is the two-line fix.

Real entry from our own SMS log this month: the same appointment reminder sent to the same Calgary number three times in ninety seconds, each one failing with error 30006, each one billed.

30006 means “landline or unreachable carrier.” Somebody had entered their office landline in the mobile field. No amount of retrying fixes that, and every retry costs money and delays the queue.

The two failures worth knowing

Most SMS code treats every failure the same way and retries blindly. That is where the waste comes from.

Fix it where the number is typed

The real fix is not in the sending code, it is in the form. Every major SMS provider has a lookup endpoint that tells you the line type — mobile, landline, VoIP — before you ever send anything. Call it when the customer submits the booking form, and if it comes back landline, say so on the spot: “That looks like a landline — we cannot text appointment reminders to it. Is there a mobile we should use?”

The customer fixes it in two seconds. Nobody discovers it three weeks later when a reminder silently fails.

Then fix the retry logic

Wherever your retries live, they should look like this:

• Permanent errors (landline, invalid number, unsubscribed) — never retry. Flag the record so a human corrects it.
• Temporary errors (handset unreachable, carrier congestion) — retry once, hours later, not seconds.
• Log every failure with its code somewhere you actually look. Ours only surfaced because someone went through the log by hand.

One more thing in the same log

The failed messages opened with Hi john,, — two commas, lowercase name. Somebody typed “john,” into a first-name field and the template added its own comma.

Trim whitespace and trailing punctuation off name fields on the way in, and capitalise the first letter when you render. It is four lines of code and it is the difference between a message that looks like it came from a person and one that looks like it came from a broken database.