Hey Alexander,
Thanks for reaching out!
There are a few different things I’m curious about here so that I can better understand your issue:
1. First, would you be willing to share a screenshot of the exact Additional Field you are trying to create in your wp-admin? I mean, specifically, the actual admin “Additional Fields” tab where you have the options for creating the field and such. This will let me see exactly how you’re creating things and will be very useful.
You can share images by uploading them to Imgur.com, Flickr.com, CloudUp.com, or any similar image-hosting site; then just share the links to those images here and I’ll take a look.
2. Can you share your “System Information” with me here? It will provide a lot of helpful information about your site, which I will use to try and recreate your exact issues. Here’s how to do this → https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Thank you!
George