Hi Aditya
I am Vijay, an Independent Advisor. I am here to work with you on this problem.
If you had your Windows 10 license activated previously, you got a digital license. You will never need the product key again once you get digital license. Since, you have a digital license, hence when you do clean install, the license information is automatically picked up from Microsoft activation servers. Windows will activate your Windows license from this information.
Make sure the version installed is same as it was previous. For example, if it was Windows 10 Home, you need to install Windows 10 Home only not Windows 10 Pro. If at any point during installation it asks for the key, choose you will do it later on / skip.
Do let me know if you require any further help on this. Will be glad to help you.