Cannot mount binds with windows source

I can't seem to mount paths originating from a Windows directory using the docker-py.
Mounting paths using docker-compose.yml

docker_client = docker.from_env()
docker_client.containers.run(
  image='ubuntu',
  command='sleep infinity',
  remove=True,
  detach=True,
  mounts=mounts
)

I always seem to get an error:

mounts = [
  Mount(target='/app/data', source=f'/c/', type='volume')
]

400 Client Error: Bad Request ("invalid mount config for type "bind": bind source path does not exist: /c/")

or

mounts = [
  Mount(target='/app/data', source=f'C:/', type='volume')
]

400 Client Error: Bad Request ("invalid mount config for type "bind": invalid mount path: 'C:/' mount path must be absolute")

or

mounts = [
  Mount(target='/app/data', source=f'C:\', type='volume')
]

400 Client Error: Bad Request ("invalid mount config for type "bind": invalid mount path: 'C:/' mount path must be absolute")

same for //c/

using a docker-compose.yml file, everything works no problemo.

I'd not be surprised if there is a mistake somewhere, but I can't seem to figure it out.
Any help is much appreciated!

Start with the Mount objects passed to docker_client.containers.run and compare their Windows source-path handling with the working docker-compose.yml configuration. Reproduce the three source forms against the Docker Engine API, then confirm the client accepts a valid Windows bind source without producing the reported mount errors.