Backport Bug 1473872 - Target API 26
We can't upload to Google Play until this is complete.
Your app currently targets API level 23 and must target at least API level 26 to ensure it is built on the latest APIs optimized for security and performance. Change your app's target API level to at least 26.
We missed the cut-off for the <26 requirement:
Google Play will require that new apps target at least Android 8.0 (API level 26) from August 1, 2018, and that app updates target Android 8.0 from November 1, 2018.