"FileID is empty" when a PDF attachment is opened.

Steps to reproduce

1. Open a eMail
2. Click on PDF Attachment

Expected behavior

PDF attachment is opening.

Actual behavior

Mail app version

5.10.7

Nextcloud version

Latest

Mailserver or service

Postfix/Dovecot

Operating system

Debian 13

PHP engine version

Other

Nextcloud memory caching

No response

Web server

Apache (supported)

Database

MariaDB

Additional info

EuroOffice is installed and working. I can also open PDF files. Based on the log file, I suspect that EuroOffice is being called to display the PDF.

Reverse Proxy Log

/apps/eurooffice/%7BfileId%7D?filePath=https%3A%2F%2Fxxx.com%2Fapps%2Fmail%2Fapi%2Fmessages%2F1689644%2Fattachment%2F2&inframe=true&inviewer=true,like Gecko) Chrome/150.0.0.0 Safari/537.36,- /apps/eurooffice/%7BfileId%7D?filePath=https%3A%2F%2Fxxx.com%2Fapps%2Fmail%2Fapi%2Fmessages%2F1689644%2Fattachment%2F2&inframe=true&inviewer=true,like Gecko) Chrome/150.0.0.0 Safari/537.36,- /ocs/v2.php/apps/eurooffice/api/v1/config/0?filePath=https%3A%2F%2Fxxx.com%2Fapps%2Fmail%2Fapi%2Fmessages%2F1689644%2Fattachment%2F2&inframe=true&inviewer=true,like Gecko) Chrome/150.0.0.0 Safari/537.36,- /ocs/v2.php/apps/eurooffice/api/v1/config/0?filePath=https%3A%2F%2Fxxx.com%2Fapps%2Fmail%2Fapi%2Fmessages%2F1689644%2Fattachment%2F2&inframe=true&inviewer=true,like Gecko) Chrome/150.0.0.0 Safari/537.36,- /index.php/apps/files/preview-service-worker.js,like Gecko) Chrome/150.0.0.0 Safari/537.36,-

nextcloud.log

{ "reqId": "31Mok1YIeVa0tHIbl7oJ", "level": 1, "time": "2026-07-08T11:13:28+02:00", "remoteAddr": "1.2.3.4", "user": "user@example.com", "app": "no app in context", "method": "GET", "url": "/apps/eurooffice/%7BfileId%7D?filePath=https%3A%2F%2Fxxx.com%2Fapps%2Fmail%2Fapi%2Fmessages%2F1691430%2Fattachment%2F2&inframe=true&inviewer=true", "scriptName": "/index.php", "message": "The app config key dav/hide_absence_settings is not defined in the config lexicon", "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/150.0.0.0 Safari/537.36", "version": "34.0.1.2", "data": [] } { "reqId": "qJC3e5SzAbYCx2n8EIE0", "level": 3, "time": "2026-07-08T11:13:29+02:00", "remoteAddr": "1.2.3.4", "user": "user@example.com", "app": "eurooffice", "method": "GET", "url": "/ocs/v2.php/apps/eurooffice/api/v1/config/0?filePath=https%3A%2F%2Fxxx.com%2Fapps%2Fmail%2Fapi%2Fmessages%2F1691430%2Fattachment%2F2&inframe=true&inviewer=true", "scriptName": "/ocs/v2.php", "message": "Config: 0 Datei-ID ist leer", "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/150.0.0.0 Safari/537.36", "version": "34.0.1.2", "data": { "app": "eurooffice" } }