Hello,
Welcome to the Prismic community, and thanks for reaching out to us.
The preview token expires once the saved information has been archived or published. The preview token generated is only valid for the information being previewed at that time. This would suggest that your trying to use an old link after the content has been changed.
It can also be related to cookies. Try to clear cookies by clicking the "X" button on the preview module to exit the preview.
You can see this thread too. We have all the information like preview troubleshoot guide in this thread:
Let me know if it still doesn't solve the issue.
Thanks,
Priyanka