[Klarna] Why does a Checkout v2 «order» request fail with the message «"Bad format: 'gender' is not part of the schema"» when a customer's gender is specified?

{
	<...>
	"customer": {
		"date_of_birth": "1982-07-08",
		"gender": "male",
		"organization_registration_id": ""
	},
	<...>
}

The Klarna’s server responds:

Bad format: ‘gender’ is not part of the schema

The «gender» field is described in the Klarna documentation:
https://developers.klarna.com/en/se/kco-v2/checkout-api#customer-object-properties

See also:

I have got an answer from the Klarna’s support:

Gender is not required for Sweden.


If you are trying to start up a KCO session for Sweden you do not need to send in the gender field.

It looks like the «gender» field is forbidden for Sweden (the documentation says it is optional, but does not say it is forbidden for some countries).