I thought that's how it works?

https://jsonbin.io/api-reference

$ cat test.json

{}

$ curl -X POST -H "Content-Type: application/json" -d @test.json https://jsonbin.io/b/new

{"success":false,"message":"Snippet parameter is missing"}

$ echo '{"snippet": "{}"}' > test.json

$ curl -X POST -H "Content-Type: application/json" -d @test.json https://jsonbin.io/b/new

{"success":true,"data":"{}","id":"..."}

Oh, you're right. My bad. Maybe they want to leave room for meta data in the future or something.