thank you for submitting the issue!
However, this seems to be a mixture of old and new json services The /api/json path is reserved for the new JSON WebServices and for those you don't need to send service parameters. In fact, the invocation model is now different as it uses REST-alike paths. Moreover, there are 3-4 different ways how you can invoke new web services, depending on what you prefer or need.
To keep long story short, I suggest to visit our official documentation about JSONWebServices:
and see how it works now (documentation on this subject is quite updated).
Also, visit http://localhost:8080/api/json in your browser, and you will see the API page and invocation call examples.