At the beginning the class Leetspeak is declared as an independent class instead of being an inheritor of Encoder. Just "extends" is needed.

Could you post your code using proper markdown and marking your post as having spoiler content? I passed the kata without problem.

Where is that line? If it is in your code, then it's wrong, check the first point you have to do:

The code must contain a Leetspeak class inherited from an Encoder abstract class.