Olhando o log a conexão com o servidor esta acontecendo e esta enviando a mensagem . Mas me parece que não esta retornando nada. Segue a mensagem do log e o link do github.
D/OkHttp: --> POST http://192.168.0.104:8080/polling
D/OkHttp: Content-Type: application/json; charset=UTF-8
Content-Length: 23
{"id":2,"text":"Renan"}
--> END POST (23-byte body)
D/OkHttp: --> GET http://192.168.0.104:8080/polling
--> END GET
D/OkHttp: <-- 200 http://192.168.0.104:8080/polling (754ms)
D/OkHttp: <-- 200 http://192.168.0.104:8080/polling (774ms)
D/OkHttp: Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
D/OkHttp: Content-Length: 0
D/OkHttp: Date: Wed, 29 May 2019 23:51:47 GMT
D/OkHttp: Date: Wed, 29 May 2019 23:51:47 GMT
<-- END HTTP (0-byte body)
D/OkHttp: {"text":"Renan","id":2}
<-- END HTTP (23-byte body)
D/AndroidRuntime: Shutting down VM
