I used below rest api code to update COMMENT for an existing Jira issue
{ "body":"test"
}
Error message : Expected a ':' after a key at 620 [character 4 line 29
Try example listed on this page using curl request, https://developer.atlassian.com/server/jira/platform/jira-rest-api-example-add-comment-8946422/
You get above mentioned error when 'JSON' data send to request is malformed or not understood properly by Jira.
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