Getting Error SQLSTATE[HY000] [2002] Connection refused on NAS Synology

Question

I am making an under construction page which is hosted on my Synology NAS.

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Answer 1

What fixed it for me.

Go to Synology Apps > MariaDB

Ensure 'Enable TCP/IP connection' is enabled above Port 3306.
Note down Domain Socket: /run/mysqld/mysqld10.sock

And as comment above.
In Web Station > PHP Settings > Edit > Core tab Search > socket

Enter domain socket example /run/mysqld/mysqld10.sock into default_sockets