The Pokemon Go App 1.1.0 and earlier have bug when you try to upgrade to the latest version from within the app.
Niantic released the Pokemon Go App update 1.1.1 on August 1. If you try to upgrade your Pokemon Go App version 1.1.0 or earlier from within the app, it fails. Niantic has left an old test-flight url in there.
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The resolution of the problem is simple. Just visit the App Store by clicking the App Store icon on your iPhone and check under updates. You will find the new Pokemon Go app version there. Click on it and you are done.
The Pokemon Go App update 1.1.1 brings only some performance improvements and it also fixes the upgrade url link.
Niantic is getting chatty now after weeks of silence. The resolution to the problem has been just posted on the support section of the Niantic Labs site. This is one of only six support pages for Pokemon Go. For an app that has about 100 million users and making $10 million per day, this is still very thin.
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The Pokemon Go trainer is not in a happy mood since the 1.1.0 update that removed the nearby feature all together. Niantic also made it harder to catch Pokemon and the legal shutdown of third party trackers like Pokevision adds to negativity.