I'm having trouble getting the answer online. I bought GTA V on my US PSN account but I play it on my PS4 from my EU PSN acc.

If I then buy a shark card off the US acc will it work with the game on my EU account? Or only with the game under my Us acc?

US purchases work with the US version of the game. DLC must be bought for the same version. You can't use japanese DLC with a US game, or mix-and-match regions.

EDIT:

It's late.  Mis-read the question.  However, I would still think it's safe to assume you had better buy the same region the game is.  Play it safe.

i need to spend another 5$ to get the 15$ free credit offer so i'm looking for something to spend it on. Bought a $2.99 shark card there. How do i use it? it didn't download anything 

if it didn't work, then it should be safe to assume that it isn't going to work with foreign accounts.  You should find something else to spend the money on.  You could have bought yourself a 10 dollar psn card for 7 dollars, and saved even more, you know?

i only found out about the latest deal tonight and it ends tomorrow. I'd already bought Shadow of Mordor or 30$, so I pre ordered BF: hardline for $60 and bought BF3 off the PS3 store for $5. So I needed to spend another 5$ and 3 cents to get the free 15$ credit. Literally nothing on the PS3 or PS4 store I want. I've bought literally everything i could possibly like. So I spent $2.99 on that shark card and made up the rest by buying shadow of mordor add ons. I bought the GTA 5 shark card and nothing happened. Took the money but no download. Like how do they work? 

Check your in-game balances, is all I can say. I haven't bought any shark cards. Didn't see a point when you could just make the money over the course of play. I tried to help, but I really don't have much an answer. read the description and see if there's a detail you missed.

According to the PSN page:

"One-time license fee for play on purchasing account’s designated, primary PS4™ system and other PS4 systems when signed in with purchasing account.

Certain limits apply to purchase, use, and redemption. See EULA www.rockstargames.com/eula and Terms of Service www.rockstargames.com/legal for details."

There is your answer.  You can't use US shark cards with EU accounts.

thank you. looks like it's only usable on my US account. Should have just got the 2.99 SOW add on instead :) Ah well at least I get my 15$ free credit now.