Embedding Zen Planner's iframes on Wix requires adding an additional Approved Site within Zen Planner. As a shortcut, you can also add a URL in the following format into Setup>Sharing & Embedding>Approved Sites: https://www-yourdomain-com.filesusr.com.
For example, if my website is https://www.getfitwithjosh123.com, I would add the following URL to Approved Sites in Zen Planner: https://www-getfitwithjosh123-com.filesusr.com
Here's what that looks like in Zen Planner: https://share.getcloudapp.com/p9u5rGDO.
If you need further guidance on this process, feel free to reach our Support Team at firstname.lastname@example.org and 866-541-3570!