You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

xtts-api-server
0.5.51

This version was deleted from PyPI around 2023-12-02. Installing fails with:
$ pip3 install xtts-api-server==0.5.51 ERROR: Could not find a version that satisfies the requirement xtts-api-server==0.5.51
View other deleted versions of xtts-api-server

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/2023-12-01/ \ xtts-api-server==0.5.51
Sign up for StableBuild to get an API key (it's free and takes <60 seconds!)

Or, download files manually

And install manually via pip:
xtts_api_server-0.5.51-py3-none-any.whl (137.7KB)
xtts_api_server-0.5.51.tar.gz (2.2MB)