Dataflow Gen2 fail to validate destination with on-premise sql database source

Hello everyone, 

I'm trying to create a dataflow gen2 in Fabric which connect to a sql server on-premise database. I successfully connect to the databse and preview data. 

But when i choose a destination which is a lakehouse in the same workspace, after the step "validating data destination target", i encouter this error : 
Microsoft SQL : A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (ID de session : 93c24660-69b0-4ded-8418-79a60b2371ac, région : france)

I have found that there is issues with dataflow and gateways. (firewalls, port..) but i didn't find the exact same issue; And i don't find very clear solution except yting to open all outbound port...

DO you understand why it won't work?