You'll need hexdump from here:
https://pointless.net/hg/hexdump/file/
curl -H "Content-Type: application/json"
-X POST -d '{"owner_id":"42","owner_name":"test"}'
http://kiosk:12345/print/box
or put your json in test.json and:
curl --verbose -H "Content-Type: application/json"
-X POST --data @test.json
http://kiosk:12345/print/box