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: 06.05.2024 @ 17:03
Script: /usercp.php?action=addsubscription&boardid=44&sid=398d95a6f8d691792430827ca37f5a0b
Referer: http://stc-board.de/usercp.php?action=addsubscription&boardid=44&sid=398d95a6f8d691792430827ca37f5a0b