Working example of API file metadata update on STATA file?

What steps does it take to reproduce the issue?
I am trying to recreate https://guides.dataverse.org/en/5.13/api/native-api.html#updating-file-metadata on some STATA file metadata I have but I have tried just about everything with no luck. I requested the existing file metadata using https://demo.dataverse.org/api/files/:persistentId/metadata?persistentId=doi:10.70122/FK2/YUUS5M/77CV8Z with no problem.

When I try to update the metadata with additional information using the following terminal commands...

export API_TOKEN=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
export SERVER_URL=https://demo.dataverse.org/api/files/:persistentId/metadata?persistentId=doi:10.70122/FK2/YUUS5M/77CV8Z

curl -H "X-Dataverse-key:$API_TOKEN" -X POST \
  -F 'jsonData={"label": "F1_SUBJECT.tab", "directoryLabel": "data/reference", "description": "This is the first file generated for this dataset and contains the participant/subject reference IDs, basic subject demographics, PA knee KL grades and reported pain in knees.", "restricted": false, "id": 1869963, "strFileName": "F1_SUBJECT"}' \
  $SERVER_URL

...I receive the following error:

{"status":"ERROR","message":"Filename already exists at data/reference/F1_SUBJECT.tab"}

This error message seems a bit odd considering I am not trying to replace an existing file, but only the metadata. What am I missing?

Start with the Updating File Metadata section of the Native API guide and reproduce the shown curl request against the reported file-metadata endpoint. Determine whether the example or the endpoint behavior explains the existing-filename error, then update the documentation with a verified working example and expected result.