What is the ruling on selling an account in an electronic game (such as Boom Beach) after reaching a high level in it, and what is the ruling on the money acquired from this sale?

If the game is free from religious prohibitions such as infidel beliefs, music, and裸 (nude/scantily clad) images, then there is no harm in playing it and selling the account that includes it. However, it is better not to preoccupy oneself with such games due to the time they waste.