Error observed while Uploading test results to Zephyr Scale via the automation API

I am trying to integrate Test automation ( Nunit framework ) to Zephyr scale via API through Team city 

I have developed a shell script which executes in 2 steps 

Step 1 : Execute Test automation scripts written using - C# Selenium Nunit Framework 

             Conversion of Nunit results to Junit results 

Step 2 : Upload or Post JUnit results to Zephyr scale via API using Token 

              https://api.zephyrscale.smartbear.com/v2/automations/executions/junit?projectKey=DSS&autoCreateTestCases=false

Here , step 2 is getting failed - please let me know the above API mentioned is correct 

Error message : " curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.
Response from server " 

Please let me know how can i get support for the above issue 

Regards,

Ravi