ERROR: org.graylog2.inputs.codecs.GelfCodec - Could not parse JSON, first 400 characters: {"host":"app","version":"1.1","short_message

The short answer is that your input is not receiving a proper JSON. Revise from who/what is sending to fix that or change the input to match what is coming in… last resort, you can make that input RAW to see what is coming in.

BTW, it’s unhelpful to just post an error message without any more detail. Here are some links to how to post:

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