This KB will give you some information, if your SMS provider can´t support Multilingual SMS Service for 2 Factor Authentication.
Currently, Zyxel 2FA products i.e. (ATP, ZyWALL, USG) series send out the SMS information text with a multilanguage code to your SMS provider. It seems that some SMS provider can´t work with this information and change the code to a correctly deliver.
It may show up like this before the verification code show up:
Content-Type: text/html; charset='UTF-8'
If that is the case, your SMS Gateway Service is not supporting Multilanguage SMS Service or you may don´t habe right license for that.
To get away from this message delivered, we are working on a new feature to deliver only the code to your customer. This require a new Firmware and a change in 2FA layout:
This is the new design of the feature after 4.60 firmware:
You can now select "Default" which will only send it out in English always and just your Text / Code.
You can select "Multilanguage File" which is performing as it is right now.