Backend launched with banner: {"result": false, "log": ["Cannot parse input"]}

[marten-seemann]

Using the example code from the README (with an added line #!/usr/bin/python3) and the following config

loglevel=7
pipe-command=/path/to/backend.py
launch=pipe

I'm getting these errors:

Feb 24 11:14:27 Backend launched with banner: {"result": false, "log": ["Cannot parse input"]}
Feb 24 11:14:27 Backend launched with banner: {"result": false, "log": ["Cannot parse input"]}
Feb 24 11:14:27 Backend launched with banner: {"result": false, "log": ["Cannot parse input"]}

I assume I've configured pdns incorrectly, but I'm not sure how exactly. It would be really helpful if the README explained how to use it.