Connection Error to Internxt/CLI webdav server

I’m glad I found this forum. – Now to my problem: I have installed a Kopia instance on an Unraid server, which I have so far used to access cloud storage from Koofr via WebDAV. However, I have reached my quota there and recently purchased a 10TB lifetime plan from Internxt. This provider offers software (Internxt/CLI) that sets up a local WebDAV server in a Docker container, from which the end-to-end encrypted files are uploaded to the Internxt servers. Unfortunately, I keep getting a connection error when I try to create a repository using KopiaUI:

When I use the same target with for e.g. Duplicati, it instantly works like a charm without any flaws/problems. But I definitely don’t want to use Duplicati! How can I find out what the exact technical issue is that’s preventing Kopia from working with Internxt/CLI via WebDAV, even though it works flawlessly with Duplicati? Which logs should I search and what should I look for to identify the specific problem? Kopia works fine with Koofr via WebDAV, but as I said, I’ve run out of space there… Thanks for any help!

Kopia v0.19.0 linux-x64
internxt/cli/1.5.3 linux-x64 node-v22.13.1

Internxt has many issues including some serious ones:

I guess you got what you pay for. It is not kopia job to support some half webdav compliant APIs.

Try to seek help on their forum maybe.

yeah, seems so, I guess. But nontheless Duplicati works without any problems though I, as already said, I don’t wanna use that for some reasons. I also tried to get help from internxt, no answer so far…