InAppUpdater sees the update, but can't install it about inappupdater HOT 4 CLOSED

Are you testing the app(version = 2) in debug mode? If that's the case you need to sign the apk with same key used to build app(version = 3) and build a signed apk. Hope this will solve your issue. If not please let me know.
The reason android OS is not able to install the update as the current app(version = 2) is not signed.

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I tried this, unfortunately this doesn't work.

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Sorry for being away. I tried the same code you have added above and was not able to reproduce the problem when I'm using signed apks(Build -> Generate Signed Bundle / APK). But I was able to experience the behavior you have stated when just running the app via Android Studio using the debug mode and just building apks(without signing)(Build -> Build Bundle(s) / APK(s))

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This is strange, but Google support says this:

Please note that we only support the update while you have downloaded your app from Google Play at least once before using the account to test in-app updates.
To solve this issue, please download app with version 1.2 in Google Play Store and upload a new apk with higher version in Alpha track. After it pass the review, you can try the in-app update again.

Unfortunatly, we are only able to assist the issue if the app is downloaded from Google Play Store instead of installing APK files manually.
Please note that the error install from other source is out of our scope. As a result, we'll still recommend you to use the In App Updates feature while the app is downloaded from our Google Play Store.

So, I downloaded 1.2 on my phone, upload 1.3 to the Google Play, and now I can update my app. But if I build signed apk with 1.2 version using the same key and download it to my phone, I can't do the same, and this is strange because you can do it. Anyway, I think it's Google's area of ​​responsibility. Thanks!

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