This can happen for a number of reasons:
1- Is the site approved for ads?
I would suggest checking your monetisation tab and emails. It may be that the platform quality team reviewed your site and found that it didn't meet the Ezoic requirements. If so then this review would show on your monetization tab, and you should have also received an email at time of review.
2- Check out this guide on Why Aren't Ads Showing Up On My Site? You can see this goes through a number of reason why ads may not be showing.