why didn't i get 10 coins when i installed lezhin :(

Did you install the Lezhin PLUS app directly from the website here: https://www.lezhin.com/en/page/lezhin_plus
If you did install that app and did not receive any coins, file a ticket through Customer Support and they'll send you the coins.

i already got the 10 coins, thanks for telling me anyway! :-)