Everything is okay with application/json:

with application/x-www-form-urlencoded though:

upd:
example of schema
requestBody:
type: object
properties:
accountId:
type: integer
required: true # in this case everything is okay
symbol:
type: integer
deprecated: true # isn't marked in application/x-www-url-encoded
...
required: # isn't marked in application/x-www-url-encoded
- accountId
- orderId