This feature doesn't appear to work any more. It may have been dependent on the old (obsolete) method OBi devices used to log directly into a user's Google account; that method was replaced by OAUTH 2.0 token authentication to perform specific, limited functions on the Google account.
There are a couple of other ways to get notified of texts:
- (Well, duh) use a forwarding cell phone number, which will receive the texts.
- Have GV email you when you receive a text.
You don't even need to use a cell phone with working cellular service. If you have an old smartphone or tablet, just install the Google Voice app on it, and it will receive text messages over WiFi, and/or receive them via Gmail.