I know the meaning of
氪 is krypton. But I find there are many people say:
Now they have got the game and played it, so they needn't buy the game now, even sometime they say so when play a free game. So how to understand the meaning of it?
I think it might originate in Japanese, where it is written as 課金, meaning that you pay real money to the game, to get some advantages (such as better equipment).
When the word come to Chinese, 課 (simplified: 课) has the same reading as 氪. So on the internet, it is sometimes written as 氪金. You might also see other forms.
I see the question has already been answered, but I want to add a method of finding the answer.
This word is in CC-CEDICT. You can search it on: https://www.mdbg.net
to make an in-app purchase in a game