You do can read it for free by logging in everyday and collect atleast 3 bonus coins. Each chapter cost 3 of them, bonus coins and "coins" [that you can get by spending real money] ← normal coins
One way to catch up faster is that you can try and read on other sites first until you reach the latest chapter then read it legally on lezhin with bonus coins. For example, chapter 77 is currently the latest on lezhin and the latest here is chapter 75. You can read it till chapter 75 then you can read the rest of the chapters on lezhin using you're bonus coins! Hope this helps. Have a good day! :D