You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.
jksandbox was reported malicious
OSV:MAL-2024-5280 - Malicious code in jksandbox (PyPI)

jksandbox
99.0

This version was deleted from PyPI around 2024-04-17. Installing fails with:
$ pip3 install jksandbox==99.0 ERROR: Could not find a version that satisfies the requirement jksandbox==99.0
View other deleted versions of jksandbox

Install through StableBuild

You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \ -i https://YOUR_API_KEY.pypimirror.stablebuild.com/2024-04-16/ \ jksandbox==99.0
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Or, download files manually

And install manually via pip:
jksandbox-99.0.tar.gz (4.6KB)