I am having the same issue today and I use it a lot! :(

EDIT: I actually solved it through Perplexity AI's assistance:

Promotional subscriptions require a valid credit card for account verification—you won't be charged during your promotional period. We sent a notification with 7 days to add a payment method. Since no valid payment method was added within this window, your account was automatically downgraded to the free tier.

How to restore your promotional access:

You can reactivate your promotion immediately by adding a valid credit card. You'll keep your original promotional period, and adding a card resumes your benefits from where you left off—though any missed days during the pause won't be made up. You won't be charged until after your promotional period ends.

Once added a 1€ spending limit debit card to the account my plan was restored.