Based on my findings, there are a few who, in the past, experienced this issue.
[Solution!] No Google Play Store Key (No OBB found and no store key) - Platform & Builds / Mobile - Unreal Engine Forums
Many solutions in this thread you could give them a try.
There is also a Youtube video that takes you through various steps to fix this issue. You could give it a watch and see if that fixes the problem.
(15) No Google Play Store Key (No OBB found and no store key) - YouTube