post https://api.fastspring.com/webhooks/keys
This call allows you to update the HMAC secret used to generate an encrypted hash of the webhook payload for a defined webhook endpoint. Please ensure your server is capable of decrypting messages with the new HMAC key before you update the HMAC secret. Your server can discard the old HMAC secret once it has been updated in the FastSpring platform.
See Message Security for more details on how to use this HMAC secret.