I m getting 405 error while accessing this Rest API https://user.name @atlassian .net/rest/api/3/issue.What could be the possible issue?
That isn't how the API calls are used - please see here for the API documentation.
The format for calls is
https://companyname.atlassian.net/rest/api/3/issue
replacing companyname with the name in your Jira URL.
Authentication is handled by passing in a 64 bit encrypted version of your email address and an API token
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