A bug currently affecting the game appears to prevent it from downloading directly via the PS4 PlayStation Store, with the game's menu simply presenting players with a 'Start' button rather than the option to download.
Attempting to download the game from the PS4 game library doesn't appear to do anything, either.
Until the issue is fixed, however, the PlayStation community has found a temporary solution that sees you forcing the game to download via an external device, such as the PS4 companion app.
If you've purchased a digital copy of Dying Light on PS4...
from VideoGamer.com - PSP Updates http://ift.tt/1BxCo82