Looks like MySQL Workbench is installed on the same computer where MySQL database is installed. When you specify 127.0.0.1 for Server in MySQL Workbench it connects to MySQL that is installed on the same computer. The same behavior refers to Skyvia. When you specify 127.0.0.1 for Server parameter, then Skyvia try to connect to MySQL server on the same computer where Skyvia is hosted. However, there is none MySQL database on this computer and you get the error.
If you want to connect to your MySQL database, you need to specify an external IP of your computer where MySQL database is located. You can find external IP by using any site which provides such functionality. For example, https://myexternalip.com/ . You should open this URL form a computer where MySQL server is installed.
When working with MySQL connections, the main requirement is that your MySQL database must be available through the Internet. When a connection to a computer in the local network takes place, it is necessary to use port forwarding.
Please contact your system administrator to make MySQL database accessible from the Internet, at least from the Skyvia's IP address (126.96.36.199), via port forwarding. For more information, please refer to https://skyvia.com/resources/docs/index.html?mysql_connections.htm