There is a critical bug in latest versions of Google Play Store application (versions 10.7.17 and 10.7.18).
This bug which we are not responsible for (Google must fix it) can cause incorrect installation of our application that leads into vibration not working inside of our application.
For more details and proof that all this is not our fault, please refer to AndroidPolice.com article: Google Play Store app licensing bug is putting developers in a horrible spot and article on XDA Developers: Latest Play Store update breaks license verification for paid apps
UPDATE (2018/07/03): Google released fixed version of Google Play Store 10.7.19 - please download the latest version, install it and and go to Mi Band Tools and press the bluetooth icon in upper right corner to resolve this issue.
If this did not help you, you must revert to previous version of Google Play Store by doing this:
We're very sorry for the inconvenience, but sadly it is not something that we can fix - we already contacted Google about this issue and asked them to fix this as soon as possible. We appreciate your understanding and we hope that you won't down-rate our application because of error on Google side. Thank you.