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: 07.05.2024 @ 01:36
Script: /usercp.php?action=addsubscription&boardid=18&sid=1354e27715c29f02fed5e6b843d9ee3c
Referer: http://stc-board.de/usercp.php?action=addsubscription&boardid=18&sid=1354e27715c29f02fed5e6b843d9ee3c