## Problem

With `AsyncClient`, passing multiple attachments under the same key fails with a malformed attachment object error. The same payload works with the synchronous `Client`, so the async file-handling logic differs. Version 1.6.0, Linux, Python 3.12.

## Verified fix

`AsyncClient` used different file-handling logic than the sync `Client` and mangled repeated keys. The maintainer fixed it in PR #35, so upgrading to the release containing that fix resolves it. Workarounds for the affected version: use unique keys (`"inline[0]"`, `"inline[1]"` instead of `"inline"` twice), or pass the attachments as a tuple of tuples rather than a list of tuples, which bypasses the SDK's dict/list checks and hands the object to `requests` verbatim. The reporter confirmed unique keys work.
Source: https://github.com/mailgun/mailgun-python/issues/33