500 Internal Server Error on Synching with Dropbox

Server replied “500 Internal Server Error” to “PUT https://mail2.tcm.marketing/remote.php/dav/files/pgehle/DropboxV2/kvt-logo_neu.png” (File not found at path: kvt-logo_neu.png.ocTransferId1320348703.part),DropboxV2/kvt-logo_neu.png ,ownCloud (2) ,260 KB,pgehle@mail2.tcm.marketing,2025-02-06T08:53:13.000,Blacklisted ,

Hi,
I try to use Dropbox inside my Account. I successfully added Dropbox to the external Storage and put my use into the “Availabel User” list.
The Dropbox Folder is shown in my OwnCloud Folder. But it is Empty (Dropbox is full).
When I put an File into the Owncloud>Dropbox Folder i get the following Error:
Server replied “500 Internal Server Error” to “PUT https://xxx/remote.php/dav/files/pgehle/DropboxV2/kvt-logo_neu.png” (File not found at path: kvt-logo_neu.png.ocTransferId1320348703.part),DropboxV2/kvt-logo_neu.png ,ownCloud (2) ,260 KB,pgehle@xxx,2025-02-06T08:53:13.000,Blacklisted

This happens even I user the Windows Client or Webconsole.
Also it doesn’t matters if I use the external or internal Serveradress.

OS: Debian 12
Webserver: Apache2
DB: mariadb
PHP: 7.4
OC: 10.15.0.2 (stable) Fresh Install
Package Source: /repositories/isv:/ownCloud:/server:/10/Debian_12 - openSUSE Download
Integrity: No errors have been found.
Ext. Storage: Dropbox