Node express POST Json document invalid json - node.js

Question

I want to send a json document to a POST link route, on the backend, my API parses the json body with the bodyparser and inserts the document into a MongoDB Collection, however I always get "invalid json". When I am using w-xxx-urlencode and pass the fields with urlencode, it works normally. The json document should be valid itself:
{"_id": "5afa7fcb01b8c6e5a83aa8f6", "Timestamp":"2020-01-01T09:01:55.128Z","PB":9191,"pot":0,"nP":4343,"L":3333,"Lze":4444,"p":5555,"ne":66666666,"Pr":7777}
I get the error:
Error: invalid json
at error (C:\Users\U500405\git\Backend_node.js-Server\node_modules\body-parser\index.js:97:13)
at C:\Users\U500405\git\Backend_node.js-Server\node_modules\body-parser\index.js:50:63
at IncomingMessage.onEnd (C:\Users\U500405\git\Backend_node.js-Server\node_modules\raw-body\index.js:119:7)
at Object.onceWrapper (events.js:313:30)
at emitNone (events.js:106:13)
at IncomingMessage.emit (events.js:208:7)
at endReadableNT (_stream_readable.js:1064:12)
at _combinedTickCallback (internal/process/next_tick.js:138:11)
at process._tickCallback (internal/process/next_tick.js:180:9)
When I am leaving out the first "_id" field,I get the error:
POST /link/err 400 2.672 ms - 724
SyntaxError: Unexpected token T in JSON at position 1
at JSON.parse (<anonymous>)
at C:\Users\U500405\git\Backend_node.js-Server\node_modules\body-parser\index.js:52:25
at IncomingMessage.onEnd (C:\Users\U500405\git\Backend_node.js-Server\node_modules\raw-body\index.js:119:7)
at Object.onceWrapper (events.js:313:30)
at emitNone (events.js:106:13)
at IncomingMessage.emit (events.js:208:7)
at endReadableNT (_stream_readable.js:1064:12)
at _combinedTickCallback (internal/process/next_tick.js:138:11)
at process._tickCallback (internal/process/next_tick.js:180:9)
in the app.js module, I initialised to use Json bodyparser:
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
My function to create the parsed json data and save in MongoDB is:
exports.create_an_FA= function(req, res) {
console.log(req.body)
var fa = new FA(req.body);
//SAVE the new instance
fa.save(function(err) {
if (err) {
console.log(err);
res.status(400);
res.send(err);
}
else {
console.log("Instanz FA in Datenbank erzeugt!");
res.status(200);
res.json({ message: 'FA-Instance created in datbase!' });
}
});
};
Why do I get the error no valid JSON data? it should switch automatically between json bodyparser x-www-urlencode and json(), depending on the body format right?
Edit:
I used the curl command to send post data as following:
curl -d "{\"Timestamp\":"\2020-01-01T09:01:55.128Z\","\PrognostizierterBetriebswert\":9191,"\posFlexPot\":0,"\negFlexPot\":4343,"\Leistungsuntergrenze\":3333,"\Leistungsobergrenze\":4444,"\posGesEnergie\":5555,"\negGesEnergie\":66666666,"\Preissignal\":7777}" -H "Content-Type: application/json" -X POST http://localhost:5000/DNZ/FA
and I get:
curl: (6) Could not resolve host: application
I tried without the escaping "\" character but then I get undefined or an empty document returned...