Access Denied on opening file from federated share?

I am running collabora and nextcloud in separate docker containers. All works well and as expected. However i have access to a second nextcloud install which shares a folder to me (no collabora at their site). I have read/write access to this folder and all files on it. When trying to open an office file on this share collabora/nextcloud shows a blue screen with “access denied” (Zugriff verboten).
As far as i can tell no errors or hints in the local or remote logs.

Why is this? Is it a limitation or a bug? What am i missing here?

Changing to OnlyOffice it works without problems.
At first i was sure that this must be a bug, but since this is not fixed since several releases of nextcloud / richdocuments / collabora i’m really uncertain if it’s a bug or some kind of misconfiguration/misunderstanding.

Could anyone please point me to the right direction?

After investigating some more i could find some error in my local Nextcloud instance:

[richdocuments] Warning: Failed to connect to remote collabora instance for 15110
[richdocuments] Error: OCP\Files\NotFoundException: Failed to connect to remote collabora instance for 15110 at
0. /var/www/html/custom_apps/richdocuments/lib/Controller/DocumentController.php line 229
OCA\Richdocuments\Service\FederationService->getRemoteRedirectURL(OC\Files\Node\File {})
1. /var/www/html/lib/private/AppFramework/Http/Dispatcher.php line 170
2. /var/www/html/lib/private/AppFramework/Http/Dispatcher.php line 99
OC\AppFramework\Http\Dispatcher->executeController(OCA\Richdocument ... {}, "index")

i understand that it tries to connect a remote instance of Collabora, which doesn’t exist. But why doesn’t it open the file local? OnlyOffice does exactly that. I’m not sure but i this was working a few months ago with Collabora, too. Is this a bug?

Both NextCloud systems trust each other via federated settings.

Does have the second nextcloud installation the documentserver of nextcloud enabled?
I will say ‘yes’ because u use his documentserver to edit the document.

Because it is a share, that wil mean, that the files still at his installation. Put your credentials in the settings (collabora) of his installation and it will be working.

No docuemnt server on second nextcloud is not installed and not enabled. That’s exactly what bothers me…