For a web application I'm developing, I want to pass data as a JSON object from a form to a pipeline pilot protocol.
While developing this (receiving) pipeline pilot protocol, I wanted to assign a protocol parameter to the "source" parameter of the JSON reader.
However, when doing so I'm receiving following error in the web application: 

Failed to save form: Unknown URL type in path name: {"0":{"key":"Project

I set the type of the parameter to StringType but also tried to switch to other types.
When first setting the parameter as a property through a pipeline pilot script, everything works fine...
Would you know what I'm doing wrong?

Thanks in advance!