Signal doesn't send verification code

I'm trying to set up Haven to send notification. During the setup, I tried to verify Signal number, but all I get was the following message:

> To continue installing, update to Signal: https://play.google.com/store/apps/details?id=org.thoughtcrime.securesms

FYI, I don't install the Signal app as noted on README.

https://github.com/guardianproject/haven/blob/e6f365ba205bc12ed4d6148a289a7f49fa236f15/README.md#L87

Start with the Signal notification setup instructions in README.md, especially the linked section, and reproduce verification without the Signal app installed. Trace the Android setup flow that handles Signal number verification and compare its behavior with the reported update message. Done means verification works as described in the README or the documentation clearly reflects the supported requirements.

Written by the indexing model from the issue text.