There are several instructions on how to add Flutter to your existing Andriod App, including the official wiki, but none of it has been done on a real Production app, thus when we were doing so, there were more challenges than we had anticipated, such as code organizing with submodules, support for AndroidX and product flavors, passing data back-and-forth similar to what you do with intent#putExtra and startActivityForResult, support plugins on which this module depends, support different routes while caching. Here is the step-by-step instruction with code example to do so.