With your suggestion, I was able to find the request payload information and see what was going on.
I had to change @Html.DropDownList("Geography_GeoCountry"
to @Html.DropDownList("GeoCountry"
then it started working.
Thanks for your help!
After applying the fix that @ismcagdas recommended here: https://github.com/aspnetzero/aspnet-zero-core/pull/3899/files/5a36a240b53342777a29d7fc4c11e5b57c5014aa
I had to apply the changes to both files: _DynamicEntityPropertyManager.js _DynamicEntityPropertyManager.min.js
Now it is working fine.
