No connet to db.
Supermetrics only allows SELECT queries, but for security reasons, you should log in with a user that has read-only access to the DB.
DB login credentials are stored encrypted within Google's servers. The database requests are made from Supermetrics servers hosted by Amazon.
For the connection to work, your database needs to accept connections from the IP address 188.8.131.52.
direct acces to db is allowed. There no any connet from this ip to dbip (in logs and with tcpdump).