as underhttps://theeventscalendar.com/support/forums/topic/google-structured-data-testing-reports-a-warning-about-knowledge-grap-events/ stated, I have entered a price. This does not appear in the structured data (see screenshot).
Google wants to pick up an Offer for Tickets, but price is not that. Also, it is a warning not an error that Google is displaying. Unfortunately we don’t have a built-in setting/feature to enable what you describe, but you can either customize it, suggest it as a feature via our UserVoice Feature Ideas, or leave it as is.
I wish I had a more simple answer for you and thanks for understanding!