Generate a new signing secret for the endpoint. The previous secret remains valid for 24 hours so your consumer can cut over safely.
During the overlap window, deliveries include multiple v1= values in
the X-Nexio-Signature header — one for each active secret.
API key with environment prefix. Use nx_test_... for sandbox and
nx_live_... for production. Obtain keys at
platform.usenexio.com/settings/api-keys.
Webhook endpoint UUID.