Failing PWR invocations, need to be handled in JSON in a better way.

The app itself might throw something like a OutOfCredit exception, and that would need to be communicated to the web client. The client needs to be able to check that an error has occurred and some of its detail.

Also, Pico might not be able to satisfy things, and for that a 400 type response is appropriate, but perhaps could be more helpful than it is currently. Perhaps there needs to be a Monitor for these failures, as some could be because of an atttempt to hack the server in question.