The steps to redeem are pretty simple in that you put in the game you want to redeem and when the game icon comes up hit +(plus) and select My Nintendo Rewards and Earn Points. I had so many unearned points I have about $6.00 in Gold Points which isn't a jackpot amount but should buy something fun on sale. Also those points expire on older games so redeem as soon as you pick up a new game.
https://my.nintendo.com/about_gold_point?lang=en-US
https://en-americas-support.nintendo.com/app/answers/detail/a_id/22312/~/how-to-earn-my-nintendo-points-for-physical-software

If you buy boutique games (limited run games for example) points may or may not work.
Yeah the error message I got with some games was it wasn't in my region.