ssms – How can I connect to my local SQL server outside my network?

Our main SQL Server instance is on a cloud server and I need to create a new server linked to a local SQL server. However, I have trouble doing it.

I tried to enable TCP / IP ports, delete all dynamic IP addresses, disable the firewall, create an incoming firewall rule on the corresponding port number , but still nothing.

It should be noted that I can not ping the local server from my external server. I guess this could play a role … Another thing to note is that in SQL Server Configuration Manager, when I click SQL Server Services and display the instance name in the right pane (SQL Server (Instance)). The "Log in as" column displays. NT Authority LocalService, maybe that's also why I can not login remotely, but I'm not sure that changing this will affect other connections?

I see this thread a lot in the messages, but I've already tried this:

I can not connect to the SQL database of my servers via an IP address

I tried to put it in the server name (instance of IP Server local server)

No matter what I try I have this error:

A network-related or instance-specific error occurred when
establish a connection to SQL Server. The server was not found or
was not accessible. Check that the name of the instance is correct and that
SQL Server is configured to allow remote connections. (provider: SQL
Network Interfaces, Error: 26 – Error Locating Server / Instance
Specified) (Microsoft SQL Server, Error: -1)