As long as you put it as your primary account on your primary ps4 you should be able to play on your US account, I can play on my UK account

I went through with downloading it last night anyways, and yeah, all is well playing from my US account. I figured it was just a difference of whether or not the system was set as the primary PS4 for both accounts.

I wasn't able to play on my US account. There's a little padlock on the icon when I log in to my US account. 

Can you switch what the primary account is on the PS4? Back and forth, I mean.

When you set up the PSN account, you were asked if you wanted your PS4 to be the primary system for that PSN account. Not that the PSN account would be the primary, but by selecting the PS4 as the primary system for the account, they share games and benefits across all accounts on the system. I'm sure there's a way to still select the PSN account to act that way. It's by that function that I can play games from both my UK and Singapore account on my US account.

Ah, got it. Thanks

Multiple accounts can be primary on a single console. So if you ever create an account for similar reasons * then always set it as primary.

*Occasionally there are price glitches on other stores, I also used to sub to USA ps plus as well as my UK one before games became the same across region