This is a transient Meta-side error that usually goes away after refreshing the page or recreating the template from scratch.
The Bïrch team has added a workaround on our side. Once on the review page, you can click "publish," which opens a pop-up window with an option to publish the ads, bypassing validation errors.
If the error persists or you need further help, please reach out to us via the chat bubble in the bottom right corner or email support@bir.ch