@Umamaheswari V Thanks for reaching out to us, is this document you are following to call the API? https://learn.microsoft.com/en-us/azure/ai-services/language-service/custom-text-analytics-for-health/quickstart?pivots=rest-api
The error message you shared indicates that you have an empty request sent, could you please check on the guidance to see if you have something missed?
Please let me know how it works.
Regards,
Yutong
-Please kindly accept the answer if you feel helpful to support the community, thanks a lot.