After searching this forum and Google, I didn't find what I was looking for. So I now following the advice to start a new topic for this (at least for me) unknown error.
The problem is coming/part off/generated (perhaps by me) from an http request node.
To explain it more: I have a device with a webpage.
It has two switches: sw_0 and sw_1.
If in the browser I type:
I can put sw_1 on.
Or: 
to put sw_1 off.
So far so good but when I now try to get info from this page with a http request node, I get this error, HPE_INVALID_CONSTANT under the node and in the debug window it shows "Error: Parse Error".
I guess I am doing something completely wrong.
[{"id":"8da0b852.8c87e8","type":"inject","z":"7b226f34.d363","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":160,"y":140,"wires":[["714af8ec.a24cd"]]},{"id":"1995a2a9.f4a055","type":"debug","z":"7b226f34.d363","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":570,"y":140,"wires":},{"id":"714af8ec.a24cd","type":"http request","z":"7b226f34.d363","name":"","method":"POST","ret":"txt","url":"http://192.168.2.200/sw_on=0","tls":"","x":350,"y":140,"wires":[["1995a2a9.f4a055"]]}]
I did this ones before with a webpage that showed some values of temperature and humidity but that seems not to work with this one.
Any ideas how to solve this? Thanks for reading.
