Connection refused, errno = 111, address = localhost, port = 57838 #0

Hi, this is the API I am using: GitHub - RootSoft/algorand-dart: Unofficial community SDK to interact with the Algorand network, for Dart & Flutter
the application I am developing on android studio with flutter in Dart, no I am not currently using any node for testing. I usually use docker sandbox for nodes, do you know a way to interface it in this case with a type of application like this?