http event collector error inputting data?

I want to try to inputting a simple event to http event collector just to test if it works. I think it was able to find the web address and also authenticate it with the token value. But I get an error with the invalid data format. What can i do to fix it? I have the following command: curl -k -H "Authorization: Splunk B86C5445-76D4-4FAF-A0FA-D8FE2FA49F79" https://localhost:8088/services/collector/event -d '{"event":"testing"}' With the followng result: {"text":"Invalid data format","code":6,"invalid-event-number":0}