Question: I'm trying to upload a version of the instant app sample code to the market with no success. I keep getting the following error: 

> 
> Your Instant App APKs do not declare a valid
>  'android:targetSandboxVersion' attribute in their AndroidManifest
> 
> 
> 

Thanks,

Answer: 
What 'vyndor' says is correct. The AndroidManifest.xml file that needs to include it is the one for the "base" feature.

If you use Android Studio 3.0 Canary 4, the android:targetSandboxVersion attribute should be set for you automatically.
You have 2 options:

1. Target API 25.
2. Add `android:targetSandboxVersion="2"` to your AndroidManifest `<manifest>` tag.