Attach Files in a test cycle

Recently we moved to Jira Cloud. I'm trying to upload a file after creating test cycle. 

test cycle creation and testcase status update is working fine. But I'm unable to uploadfiles into cycle. I tried using "custom" execution API's. But no success.

The file upload was working fine in server and i used /testresult/{testResultId}/attachments format.

Is there any way we can upload files in to an execution. 

I'm using https://api.zephyrscale.smartbear.com/v2/automations/executions/custom