BackWPup doesn’t work

Hi guys,

I am suffering from problems with the plugin BackWPup (free version). It used to work for quite a while and I was able to save the backup in my dropbox. Unfortunately, by now it stoped working despite me deleting all other files in the dropbox. The error message is:

[24-May-2019 15:21:19] 16227 Dateien mit 652,96 MB im Archiv.
[24-May-2019 15:21:24] 1. Versuche, das Backup zur Dropbox zu senden …
[24-May-2019 15:21:24] /mnt/web412/e2/03/59871203/htdocs/wp-content/plugins/backwpup/inc/class-destination-dropbox-api.php: Dropbox-API: (400) Bad input parameter: Error in call to API function "users/get_current_account": This app is currently disabled.
[24-May-2019 15:21:24] 2. Versuche, das Backup zur Dropbox zu senden …
[24-May-2019 15:21:25] /mnt/web412/e2/03/59871203/htdocs/wp-content/plugins/backwpup/inc/class-destination-dropbox-api.php: Dropbox-API: (400) Bad input parameter: Error in call to API function "users/get_current_account": This app is currently disabled.
[24-May-2019 15:21:25] 3. Versuche, das Backup zur Dropbox zu senden …
[24-May-2019 15:21:25] /mnt/web412/e2/03/59871203/htdocs/wp-content/plugins/backwpup/inc/class-destination-dropbox-api.php: Dropbox-API: (400) Bad input parameter: Error in call to API function "users/get_current_account": This app is currently disabled.
[24-May-2019 15:21:25] FEHLER: Schritt abgebrochen: zu viele Versuche!
[24-May-2019 15:21:25] 1. Versuche, die Datenbank zu prüfen …
[24-May-2019 15:21:25] Datenbank-Check fertig!
[24-May-2019 15:21:25] 2 alte Log-Dateien gelöscht
[24-May-2019 15:21:25] FEHLER: Job mit Fehlern beendet in 904 Sekunden. Um eine korrekte Ausführung zu gewährleisten, müssen Sie die Fehler beheben.

Can anybody help me to indentify the issue?

Thanks and BR
Constantin