Could be a weird toml thing, I’ve had success with this format (watch your white space)
[services.ports.http_options.response.headers]
Via = false
X-Powered-By = false
(I’m not sure if the Fly Proxy ignores this setting for certain headers, such as the request ID - someone can hopefully answer that if it becomes an issue).
Make sure you’re running a fly deploy
after making any changes here.