Bitfinex api v2 not returning candles
The problem might be, that the JSON data does not contain line breaks. I was facing the same issue. My 'subscribe' call had no effect until I added line breaks to the JSON data. I haven't even gotten an error message back from the API.

You could use JSON library for Java which will handle the correct formatting for you.

Please note, there are some existing Libraries for Bitfinex and Java. You don't need to implement the API calls on your own. 


https://github.com/timmolter/XChange (this one uses the REST API)
https://github.com/jnidzwetzki/bitfinex-v2-wss-api-java (this one uses the Websocket API)