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: 29.04.2024 @ 08:11
Script: /usercp.php?action=addsubscription&threadid=846&sid=8090dd4fbf5ecd2fa7323ffc9286d790
Referer: http://stc-board.de/usercp.php?action=addsubscription&threadid=846&sid=8090dd4fbf5ecd2fa7323ffc9286d790