PSCONFIG.exe Configuration of SharePoint Products failed. Configuration must be performed before you use SharePoint Products. A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible
An exception of type System.Data.SqlClient.SqlException was thrown. Additional exception information: 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: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
Check your connection string in HKEY_LOCAL_MACHINE > SOFTWARE > Microsoft > Shared Tools > Web Server Extensions > 16.0 > Secure > ConfigDB