Deploy fails: AttributeError: module 'marshmallow' has no attribute '__version_info__'

I’m updating a Django app that has been up on fly.io for several months. When I run the fly deploy it consistently fails with the error

AttributeError: module 'marshmallow' has no attribute '__version_info__'

on the release command

release_command: python manage.py migrate --noinput

The error appears to come from the line

from environs import Env

in my settings.py file

Problem solved

Version 4 of marshmallow deprecated attribute. Forced usage of older version in requirements.txt