What you are seeing
The code scans, the messaging app opens, but the message is addressed to the wrong number, or the prefilled text is missing or wrong. The scan worked, so the fault sits in the SMS payload: the number, the country code, or the message text. A wrong number is a serious failure, because a visitor can send a private message to a stranger. The fix is to decode the payload and to check every character of the number before anyone uses the code again.
Likely causes
1.
Wrong number in the payload — A digit mistyped in the payload sends the message to a different number. Test: decode the payload and compare the number digit by digit with the intended number.
2.
Missing or wrong country code — A number without a country code, or with the wrong one, can route to a different person or fail. Test: check the country code in the payload.
3.
Formatting characters breaking the number — Spaces, brackets, or dashes inside the number can break the parsing on some phones. Test: compare a plain-digit version with the formatted version.
4.
Non-standard SMS payload format — A hand-typed SMS payload can use a separator or field order the phone does not recognise. Test: compare the payload with the standard SMS format.
5.
Message text lost or garbled — A message with special characters can be dropped or garbled if it is not encoded correctly. Test: try a short message with plain characters and compare.
Step-by-step fix
1. Decode the payload and write down the exact number and message it carries.
2. Compare the number digit by digit with the intended number, including the country code.
3. Rebuild the SMS with the SMS generator, using plain digits for the number.
4. Scan the rebuilt code and read the drafted message without sending it.
5. Fix any field that differs, and retest.
6. Retest the final code on two phones and confirm the number and message are correct.
Putting this into practice
In practice, a wrong number is the failure to take most seriously, because a visitor can send a private message to a stranger before anyone notices. Check the number digit by digit, include the country code, and read the drafted message on a test phone before printing. Never let a wrong-number code stay in circulation while you investigate. Keep a short note of what you tested, what failed, and what you changed, so the next person starts from evidence rather than guesswork. A fix that is written down survives staff changes and reprints; a fix that lives only in memory gets repeated.
Common mistakes to avoid
- Letting a wrong-number SMS code stay in circulation while investigating the cause.
- Reprinting the full run before a single proof passes, which turns one failure into many.
- Testing on one phone in ideal conditions instead of two phones in the real conditions where a code that scans but the SMS goes to the wrong number will be used.
- Changing the artwork and the placement at the same time, so you cannot tell which change fixed a code that scans but the SMS goes to the wrong number.- Skipping the proof test because the change looked small, when small changes cause most repeat failures.
Quick checklist
- The decoded number matches the intended number digit by digit
- The country code is correct
- Scanning drafts the right message on two phones
- The corrected proof passes on two phones in the real conditions
- The fix is recorded in the job file so the next reprint starts from a proven setup
- Every printed copy is checked against the approved proof
- The proof is retested after any later change to the link, design, or placement
Related tools and guides
- [SMS QR code generator](/sms-qr-code-generator)
- [QR payload inspector](/qr-payload-inspector)
- [QR offline verifier](/qr-offline-verifier)
- [QR scan log](/qr-scan-log)
- [QR safety checker](/qr-safety-checker)
- [blog](/blog)
