Hello Inhee Kim,
Thanks for your question.
Sometimes the activation email from Microsoft might land in the spam or promotions folder.
Look at a similar issue here with a guide that mat be helpful: https://learn.microsoft.com/en-us/answers/questions/1822192/azure-grant-claimed-but-didnt-receive-email-to-act
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola