Generates a new signing secret for this endpoint. The new secret takes effect immediately — update your server before rotating.
Echo API key — format: echo_<64 hex chars>. Returned once on signup.
New secret
New secret shown once. Update your server's HMAC verification immediately.
"whsec_a1b2c3d4e5f6789012345678901234567890123456789012345678901234abcd"