This is if you have an Android phone + Google play store (haven't tried on PC + Google play store and I don't think it works on iPhone).
1. You can buy gift cards (Google Play Store gift cards) for the play store and you can load it to the play store and purchase coins on the Lezhin app. IMPORTANT: you HAVE to buy it in the regular Lezhin app NOT on the Lezhinplus app. The plus app doesn't take Google play store credit but it will update your coins in there as long as you use the same account.
2. Get Google Rewards app from the play store, you answer surveys and they give you Google play store credit. It's not much but it adds up! Got around $15 after saving up for a couple weeks and was able to purchase coins with it.
3. PayPal
4. If you go to anime conventions and Lezhin has a booth GO! They sell gift cards for coins and they include awesome posters like from Lover Boy, Blood Bank, Royal Servant, Killing Stalking, etc! Went to Anime Expo and was able to get posters of my favorite ones along with coins! (≧∀≦)
ALSO: I recommend that you switch to the Korean version everyday to get points and coin rewards for logging in everyday. It's 1 coin every so often but it helps and the points help get discounts on coin purchase. It resets when you purchase coins but it definitely comes in handy. Take advantage of end of the month coin sales, discounts!
So these are a couple of ways of buying coins without inputting your credit card directly into your Lezhin account, there might be other ways too but this is how I do it! Hope it helps!
I read a comment that you don't need a credit card to purchase coins to buy the chapters on Lezhin. What other method is there??