Have to buy already purchased app.

So i recently decided i wanted to download Bloons TD 5 HD on my phone as a way to kill time, i had already bought it on my iPad air 2 and was signed into the same apple id so i should just be able to download it but it says i have to buy it a second time again. I have checked in my phones "Purchase History" and it has confirmed that in 2016 i did buy the game so why cant it recognise that i do not need to purchase it again? The images below are proof that i have purchased it on my iPad and that i cant on my phone.