How to include a .yaml in Python3.8 package distribution

Question

My directory structure is as follows:

global_toolkit/
    - setup.py
    - MANIFEST.in
    ... 
    - global_toolkit/
        - main.py
        - protocol.yaml
        ...

The package is hosted using pypi-server and then installed by a service using pip. protocol.yaml is not in the distribution:

[Errno 2] No such file or directory: '/app/.heroku/python/lib/python3.8/site-packages/global_toolkit/protocol.yaml'

My MAINFEST.in (I've seen different formats on different tutorials. I tried them all...)

include global_toolkit/*.yaml
include *.yaml
recursive-include global_toolkit *

I've also tried to use setup.py:

files = ["global_toolkit/*"]

setuptools.setup(
    ...
    packages=['global_toolkit'],
    package_data = {'global_toolkit': files},
    ...

It's difficult to figure out what isn't working here. Help appreciated.