I was able to reproduce the issue here: link.
Root Cause
The OpenAI compatibility API endpoint does not handle lowercase header names properly, which is common in most HTTP client libraries.
@braincore Most HTTP client crates in Rust rely on the http crate, which always sends headers in lowercase. However, with reqwest, you can enable title case with following code
let client = Client::builder().http1_title_case_headers().build()?;