How to debug in vscode with mago-mi?

[Domain via Digitalmars-d-learn]

Could anyone show me how to debug in vscode with mago-mi?
I have installed vscode with Native Debug, SDLang. I have tried 
dlang-vscode and code-d.

My tasks.json:
{
     "version": "2.0.0",
     "command": "dub",
     "type": "shell",

     "presentation": {
         "echo": true,
         "reveal": "always",
         "focus": false,
         "panel": "shared"
     },

     "tasks" : [
         {
             "taskName": "build",
             "group": {
                 "kind": "build",
                 "isDefault": true
             },
             "args": [],
             //Pattern match DMD error messages
             "problemMatcher": {
                 "owner": "d",
                 "fileLocation": ["relative", "${workspaceRoot}"],
                 "pattern": {
                     "regexp": 
"^(.*)\\((\\d+),(\\d+)\\):\\s+(Warning|Error):\\s+(.*)$",
                     "file": 1,
                     "line": 2,
                     "column": 3,
                     "severity": 4,
                     "message": 5
                 }
             }
         }
     ]
}

And my launch.json:
{
     "version": "0.2.0",
     "configurations": [
         {
             "name": "Debug",
             "type": "mago-mi",
             "request": "launch",
             "target": "./bin/app.exe",
             "cwd": "${workspaceRoot}"
         }
     ]
}

I have placed mago-mi.exe in PATH.

I can build app.exe successfully. But when I click the debug 
button, nothing happen.