Hi Sibananda,
Thank you for reaching out to us,
could you help which account are you using to activate P2 license in your default tenant personal account or work/school account ?
Also did you get a chance to refer these QnA posts where similar issue has been discussed - https://learn.microsoft.com/en-us/answers/questions/1464265/i-cant-activate-the-trial-of-microsoft-entra-id-p2
If the above posts doesn't help, help me with more details like screenshot at time of issue so that I can better understand the issue and assist you.
Kindly accept answer , if it helps
Thanks
Deepanshu