I have reported the same issue about a year ago, unfortunately, it still does happen.
In Chrome secret mode, I can access the Play store page, but after I log in to purchase the app, it just shows me the message, “We’re sorry, the requested URL was not found on this server.”.
I believe that your apps support SM-N50N and since you removed all device restrictions of the Ultimate, Probably it is the region problem although you have mentioned that South Korea is not on the regional restriction lists.
Could you check if there is anything that is related to the regional issue?
South Korea is on the approved list:
I’m not sure why it wouldn’t let you buy the game. Do you maybe have parental controls enabled on your phone?
It is not enabled when I checked.
I tried on other’s devices too and the result was same. So I believe that your games are basically cannot be accessible in Republic of Korea.
Can you contact Google to find out what is going on? Probably not rating issue since I can access other games which are not yet rated.
I’m unable to find back Siralim 1 in the Google Playstore, not even when I search for Thylacine Studios, LLC.
It’s not a big issue for me because I bought it long ago so I can find it in my library list. But still it’s strange that only Siralim 2 and 3 are visible in playstore.
I was told by multiple people that 1 was removed due to bug issues. Made me a little sad because I wanted to get all of them, but I understand.