Inside the .vscode folder, create a file named launch.json.

In the launch.json file, add a configuration object for each flavor. 
Each configuration has a name, request, type, program, 
and args key.

"version"

"0.2.0"

"configurations"

"name"

"free"

"request"

"launch"

"type"

"dart"

"program"

"lib/main_development.dart"

"args"

"--flavor"

"free"

"--target"

"lib/main_free.dart"

],

"compounds"

[]