@mnowak Looks like rasa and aoihttp (a rasa depencency) require multidict < 5.0, whereas sanic (another rasa dependency) requires multidict >= 5.0, so there’s no way for Pipenv to lock to one version (as they are mutually exclusive).
If you’re not worried about locking the dependency tree, rather you just want to use Pipenv for familiarity, you could try:
pipenv install rasa --skip-lock
and then pipenv shell or pipenv run xxx.
There’s some relevant discussion on Stack Overflow here: