Getting this error running the Heroku example from the README:

    $ db-to-sqlite $(heroku config --app myappname | grep HEROKU_POSTG | cut -d: -f 2-) \

https://stackoverflow.com/a/66794960/6083 explains why:

SQLAlchemy 1.4 removed the deprecated postgres dialect name, the name postgresql must be used instead now. The dialect is the part before the :// in the URL. SQLAlchemy 1.3 and earlier showed a deprecation warning but still accepted it.

To fix this, rename postgres:// in the URL to postgresql://.