Need help regarding PS3 Digital version

Hey guys!
Here's the thing: my brother wants to play with me, but he doesn't have a PC or a PS3/4. I told him i would lend him my PS3 once i upgraded to PS4, so he can play. So i upgraded my game and used the code to download it on PS4. My PS3 was left with the game installed, so i figured my brother could just buy another digital copy from his account and access it. However, whenever i try to enter from his account, a message pop up saying that i need a PSN code or a promotion code and that re-install is not required.
What i'm trying to ask is that if it's possible to re-buy the game again on a PS3 that has the game installed already from another account. Because the digital version doesn't come with codes, we are trying to figure out if re-buying means that we can access the game from his PSN account, or if the game can only be used once on a single PS3.
I've searched everywhere for an answer and no one seems to know exactly how this works.

It should be fine to go ahead and purchase. I had the beta version downloaded on my PS3, but still had to purchase the digital version in order to play. Prior to purchase I got the same message about lacking a code.

It is tied into the psn network so ya buy the game and reg to his psn account.

Thanks guys! I bought it and works perfectly fine!
So i guess the copy you buy on PSN can only be used in the same account. I was so worried it wouldn't work, but it did :)