Generic form pages only. Changes only the keys you send.

fields is the whole ordered list: a field you leave out is removed. A field you send keeps every form builder setting the API does not name. A field cannot change type. To rename a field and keep its submissions, send it under the new name and add { old_name: new_name } to renames; migrated reports how many submissions moved.

A change that removes a field or an option that already has submissions returns 409 with requires_confirmation and impacts (each removed field or option and its submission count). Send the same request with confirm_removals: true to save it. This is the same check the form builder makes before it saves.

Custom property fields are { property, label, required }, as in POST. They keep their names and cannot be renamed. Their options always follow the property.

A field read from GET can be sent back unchanged, so a client can read fields, change one entry, and send the whole list.

Forms with parts the API cannot describe (HTML blocks, subforms, conditional fields, builder only field types) return fields: null in GET and refuse a fields change with 409; name, title, description, and published still change. Pages that are not generic forms return 409.

The admin who created the API key must have the pages.manage permission in the page's scope.