Http module: "invalid character '<' looking for beginning of value"

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With Wireshark I found out that the GET string ends up like:
http://192.168.13.50:8080/xml/json.php%3Fmode=infomin

So the reply of the SmartMeter is 404 page not found because of the %3F in the URL.
The big question is also how to get the ? in the URL instead of %3F replacement...