FSTL003 - Fastly API TLS Error

Agent error code #FSTL003 indicates the TLS handshake with the Fastly API failed: the certificate could not be verified, was invalid, or did not match the host.

Common causes include:

• A TLS-inspecting proxy presents its own certificate and its CA is not in the agent host's trust store
• The agent host's CA bundle is out of date
• An API base URL override points at a host with a self-signed certificate

Steps to Resolve

1. From the agent host, run openssl s_client -connect api.fastly.com:443 and read back the certificate chain
2. If a corporate proxy terminates TLS, install its CA certificate in the agent host's trust store
3. Only as a last resort, and only for a non-production override, enable Insecure on the backend to skip verification