Function relay_envelope 

pub async fn relay_envelope(
    client: &Client,
    upstream: &str,
    body: Bytes,
) -> Response

Relays a Sentry envelope verbatim.

The body is passed through untouched — it is a complete envelope the browser SDK built, carrying its own stack trace, breadcrumbs and release. The destination comes from the configured DSN rather than from the envelope header, so this cannot be pointed at an arbitrary Sentry project.