Hey @aliyazdi75,
Thanks for your post and once again, apologize for the delay. Have you visited the flutter application guide from this forum? I see some differences against the flutter.dev sample guide that could be of help. I am not a flutter expert but will take a look at this dbus concern you have and will come back to you hopefully with a solution. If needed sample guides should be updated as well.
I suggest you work locally before pushing the snap to the store until you are sure about what your snap needs and why. You could start with devmode, and then switch to strict confinement once you get such understanding. Please see this video for further details.
I also suggest installing the snappy-debug snap, which will help you troubleshoot and even suggest interfaces your snap might need (I mentioned this tool and other docs in the other post you created).