Unicode OTP Not Sending? Encoding Issue Fix
Unicode (Hindi, Tamil, etc.) OTPs failing to send: GSM-7 vs UCS-2 encoding, DLT template language registration, and why a single accented character breaks delivery.
StartMessaging Team
Updated
A single non-GSM-7 character can break your OTP delivery. This guide explains the encoding rules and the registration step that most teams miss.
Why Unicode OTPs Fail
- Template registered as GSM-7 but body has Unicode chars.
- Operator scrubber rejects on encoding mismatch.
- Multi-part fragmentation drops on some carriers.
GSM-7 vs UCS-2
- GSM-7: 160 chars, basic Latin.
- UCS-2: 70 chars, full Unicode.
- One Unicode char anywhere = whole SMS becomes UCS-2.
DLT Language Registration
Hindi / Tamil / regional templates need a separate DLT registration. See our regional-language SMS guide.
Invisible Unicode Characters
- Curly quotes from copy-paste.
- Em dashes from auto-correct.
- Zero-width joiners.
- Non-breaking spaces.
Run your template through a GSM-7 validator before submission.
Fixes
- Replace curly quotes with straight quotes.
- Use ASCII-only template body if possible.
- For Hindi templates, register them explicitly under regional category.
FAQ
StartMessaging handles encoding consistency on the template side; your body stays GSM-7 unless you explicitly opt into Unicode.
S
StartMessaging Team
StartMessaging Team