I've successfully created a new field on the frontend with an
extension_attribute by this documentation.
My problem is that where should I hook the extension attributes on the admin page?
The shipping method is set by
Magento_Sales/order/create/scripts.js with the
But this is a prototype file, I can not hook on it with mixin, since it has no return value.
How can I add/get the
extension_attributes with my value?