This usually means the OBB file is in the wrong folder. Double-check that it is in Android/obb/ and not nested inside another folder.
To unlock the full game (remaining missions and the OBB data expansion), there is a single in-app purchase of approximately $14.99 / £12.49 / €14.99 Total Size: The game requires roughly hitman blood money obb apk
The older Hitman: Blood Money Java-based mobile versions from 2009 are NOT the same. The modern OBB APK is for the full 3D PC port. This usually means the OBB file is in the wrong folder