Please do it in this exact order, using the same Google account for every step:

1. Join the Google Group first:
https://groups.google.com/g/deluno-testers

2. Then open this Web opt-in link and tap “Become a tester”:
https://play.google.com/apps/testing/com.deluno.app

3. After the opt-in page says you are a tester, install Deluno here:
https://play.google.com/store/apps/details?id=com.deluno.app

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