"a foreign key constraint fails" on a nullable FK

Hello, I'm testing Radzen and I'm having a very basic error, but can't find a way around it.
I have a MySQL DB with a table that has a nullable field with a 1 to many FK (the table is in the 1 side).

I can't find a way to set the value to null without getting a "a foreign key constraint fails" error when adding a record... I have tried deleting the dropdown field, unchecking "visible" and "is required", and setting null in the default value... nothing is working.

Any help would be appreciated... thanks!

Usually a nullable foreign key is set to null when you delete the parent record (cascade delete).

Thanks for your response.
Can't it be created without a parent record? I'll use this if not: https://www.radzen.com/documentation/many-to-many-crud/ but I don't really need a many to many relationship, just a 1 to many that is nullable.