@MarkNagy I've been able to subscribe and it does work perfectly on my mobile device without Google Play Services installed as you said so thank you very much for that tip.

Perhaps the text in the app could be a little clearer as it specifically refers to Google accounts and I wouldn't have realised a desktop subscription would work fine without your help.

I'm not sure what security risk there would be with having the app hosted by Windy on the Windy.com website, given that the apk can already be extracted from other places. It could include a warning that most users should continue to download it from the play store. https://signal.org/android/apk/ is a good example of this.