What was going on
A clean `pip install modern-treasury` in a fresh venv (python 3.13), then `modern_treasury.ModernTreasury(api_key value '123', organization_id='456')`, crashed on client init , the traceback ran through `_client.py` into httpx internals. The httpx dependency wasn't pinned, so a new httpx release broke the SDK. Version 1.43.1 was supposed to contain the fix but hadn't published to PyPI (the publish had failed).
What fixed it
Two things went wrong: an unpinned httpx broke client construction, and the fixed release (1.43.1) failed to publish to PyPI. Workaround confirmed by the maintainer: `pip install httpx<0.28`, or install the SDK straight from GitHub. The real fix shipped in v1.44.0 , the reporter confirmed 1.44.0 is picked up by default and contains the fix. Source: https://github.com/Modern-Treasury/modern-treasury-python/issues/570