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: 09.05.2024 @ 08:56
Script: /usercp.php?action=addsubscription&boardid=5&sid=4fb152146c3d2a726e4ea8e9786e0c6c
Referer: http://www.stc-board.de/usercp.php?action=addsubscription&boardid=5&sid=4fb152146c3d2a726e4ea8e9786e0c6c