Function error_chain_string 

pub fn error_chain_string(e: &(dyn Error + 'static)) -> String

Render an error’s full cause chain (Display of every level, : -joined).

format!("{e}") on a reqwest::Error prints only the top level — e.g. error sending request for url (…) — and silently drops the source that says why (operation timed out, dns error, connection refused, …). That cost a real postmortem hours; always surface the chain.