Hello @Bitthal Bhai Patel , I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.
Issue: code": "404", "message": "Resource not found
Solution:
Working on REST API for developing chrome extension. Figured out the solution using https://<your-region>.api.cognitive.microsoft.com/text/analytics/v3.1/sentiment?opinionMining=true
Thank you again for your time and patience throughout this issue.
Regards,
Vasavi
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.