secret-key is an optional header. It is required when you need to Update a Private record. You can find your secret-key on the API Keys page after signing-in.
[2] JSONbin UPDATE API Reference | JSONbin.io | Free JSON storage and JSON hosting service. Ideal for small scale Web apps, Websites and Mobile apps, , https://web.archive.org/web/20181118155404/http://jsonbin.io/api-reference/bins/update
[3] >>2 では secret-key
だったのが >>1 の今の版では
X-Master-Key
と X-Access-Key
になっている模様。
secret-key
X-Master-Key
X-Access-Key
X-Master-Key
X-Access-Key
[7] Help & Support - JSONBin.io, https://jsonbin.io/support/tags/access-keys-api#questions