“SMS is a best effort protocol, meaning your carrier will do its best effort to deliver the message to you but there may be failures. Sometimes due to high network traffic or spam filters you won’t receive the text message.”
SMS can’t be relied on, and at the moment my carrier is not supported by your provider, so I can’t authenticate my phone anymore.
If the SMS is not received, it would be best to offer the option to call instead. At the moment the only option is to contact support.