Found this question while researching a "ERROR JsonLineBreaker" "Unexpected character" events in my Splunk. I tried to re-create the error using Splunk 7.1.2 but the provided curl command fails due invalid JSON.
curl -k https://localhost:8088/services/collector/event -H "Authorization: Splunk ${TOKEN}" -d '{"event": "Hello, McKinley High!", "sourcetype": "_json", "fields": {"club":"glee", "wins",["regionals","nationals"]}}'
{"text":"Invalid dataformat","code":6,"invalid-event-number":0}
"wins" is followed by a "," when it should be a ":". Correcting the issue yields a "Success" message w/ no "ERROR JsonLineBreaker" logged.
curl -k https://localhost:8088/services/collector/event -H "Authorization: Splunk ${TOKEN}" -d '{"event": "Hello, McKinley High!", "sourcetype": "_json", "fields": {"club":"glee", "wins": ["regionals","nationals"]}}'; echo
{"text":"Success","code":0}
FWIW, the JSON typo came from Splunk's "Explicit JSON fields" example at:
http://dev.splunk.com/view/event-collector/SP-CAAAFB6
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