Print JSON decode errors for debugging

src/main.rs

@@ -144,6 +144,7 @@ async fn main() -> std::io::Result<()> {
                                 mime.type_() == mime::TEXT && mime.subtype() == mime::PLAIN
                             })
                             .error_handler(|err, _req| {
+                                eprintln!("Error while decoding JSON: {:?}", err);
                                 // create custom error response
                                 error::InternalError::from_response(
                                     err,