Hello Anupama Sobha,
Welcome to the Microsoft Q&A and thank you for posting your questions here.
I understand that your CLU throwing exception message "xxxxxx" is not a valid CLU subscription key from BOT framework.
If the key is copied correctly from Azure, I will advise to double-check your appsettings.json file for any discrepancies and if you're using environment variables, makes sure they are correctly set and accessible by the application. Most importantly, make sure you're using latest version of the Bot Framework SDK, and your key format is supported with it.
I hope this is helpful! Do not hesitate to let me know if you have any other questions.
Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful.