No, there's no proxy.
I'm importing the package, building
it, and uploading it. The build and upload complete, but I get a 408 error.

When I refresh the package list, the package is present.
The md5sum is identical between the built package and the one that's present on the machine, as seen in the console...

After increasing the Nginx time_out values, I now get a 408 error at the end of the upload.

Enterprise edition
console 2.2.3.12481 on Windows 10 Pro,
Wapt server 2.2.3.12481 on Ubuntu 20.04.

In the server directory /var/www/wapt, I do have a file named test-windows10-upgrade_10.0.19044-102_x64_windows_6.1_PROD_fr_83731b9867d9448e5909da66426ba8b0.wapt.

But the upload (which...

I'm trying to use this package:
https://store.wapt.fr/store/details-tis-windows10-upgrade-template_0-110_windows_6.1_PROD.wapt

It says:
You must run the "update-package" and the "build-package" for each required language before deploying the package.

I don't quite understand the "build-package" part...