Trading coins in game

I saw some guys trading coins per gold in game, is it illegal? If yes, Is there anyway to trade coins outside the game? If no, how am i supposed to get those coins with gold? thx

I'm not english, sorry for any mistake

You can use trading section in store on website to put your items and gold for sale for coins.

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Originally Posted by anyone0

You can use trading section in store on website to put your items and gold for sale for coins.

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Where exactly? i didn't find in the store

Select currency - coins, select service - trading.