For the online sandbox environment, you don't need server and serverinstance, they're automatically retrieved from your Azure AAD acount.
The launch.json file is the following:
{
"version": "0.2.0",
"configurations": [
{
"type": "al",
"request": "launch",
"name": "Microsoft cloud sandbox",
"startupObjectId": 22,
"startupObjectType": "Page",
"breakOnError": true,
"launchBrowser": true,
"enableLongRunningSqlStatements": true,
"enableSqlInformationDebugger": true
}
]
}