SQL-DATABASE ERROR

Database error in WoltLab Burning Board (): Link-ID == false, connect failed
mysql error: Connection refused
mysql error number: 2002
mysql version: unknown
php version: 5.6.40-57+0~20211119.60+debian9~1.gbp8a9bd1
Date: 05.05.2024 @ 15:07
Script: /usercp.php?action=addsubscription&threadid=258&sid=e30bb2afa3e1c319843fbe9f74070b1c
Referer: http://stc-board.de/usercp.php?action=addsubscription&threadid=258&sid=e30bb2afa3e1c319843fbe9f74070b1c