Why dub doesn't see the source folder?

Question

I wanted to run my first project with dub. I initialized the project with dub init sandbox', then ran it with dub run. But dub said this:
Configuration 'application' of package sandbox contains no source files. Please add {"targetType": "none"} to its package description to avoid building it. Package with target type "none" must have dependencies to build.

I don't understand, why does it happen because I have source folder in my project. Here's a project tree:

• sandbox
  • source
    • app.d
  • dub.json

And dub.json file:

{
    "authors": [
        "MAX_PC"
    ],
    "copyright": "Copyright © 2021, MAX_PC",
    "description": "A minimal D application.",
    "license": "proprietary",
    "name": "sandbox"
}

EDIT: This is a whole output

D:\DEVELOPMENT\[ D ]>dub init sandbox
Package recipe format (sdl/json) [json]:
Name [sandbox]:
Description [A minimal D application.]:
Author name [MAX_PC]:
License [proprietary]:
Copyright string [Copyright ┬й 2021, MAX_PC]:
Add dependency (leave empty to skip) []:
Successfully created an empty project in 'D:\DEVELOPMENT\[ D ]\sandbox'.
Package successfully created in sandbox

D:\DEVELOPMENT\[ D ]>cd sandbox

D:\DEVELOPMENT\[ D ]\sandbox>dub run
Configuration 'application' of package sandbox contains no source files. Please add {"targetType": "none"} to its package description to avoid building it.
Package with target type "none" must have dependencies to build.

Answer 1

The problem is solved! Spaces in the path to the project were the reason! So, don't write paths like me: D:\DEVELOPMENT\[ D ]

Answer 2

Dub created a new project sub-folder with name sandbox. Assuming your original project folder was myproject, then you need to use dub run at myproject/sandbox. You can move the contents to the project root folder or run dub init at your desire project location, no second argument.