Pip 'Could not find a version that satisfies the requirement'

We just started getting this today.

602 Looking in links: /home/travis/.cache/wheelhouse
603 Collecting Pyzotero==1.4.16
604 File was already downloaded /home/travis/.cache/wheelhouse/Pyzotero-1.4.16-py2.py3-none-any.whl
605 ERROR: Could not find a version that satisfies the requirement requests>=2.21.0 (from pyzotero)
606 ERROR: No matching distribution found for requests>=2.21.0

Nothing particularly changed about our builds (and I tried re-starting an old build and suddenly got it there as well). I can install both requests>=2.21.0 and Pyzotero locally without any trouble, so it seems like it could be a problem between Travis and PyPi? Is anyone else seeing something like this?

https://mail.python.org/archives/list/pypi-announce@python.org/thread/DIWIYIMGAOHDWQXXUZW44YRSW7UYQ4CA/?

Super helpful, thank you. That’s likely our problem.

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