How to create an empty Hosted Feature service using the ArcGIS REST API

I agree the API reference isn't great at explaining the whole workflow. Let me try to help.

This endpoint is only accessible to the content owner and members who are assigned the default administrator role

To use that endpoint, you need to use a token created with permissions to create hosted content (like an editor user type in ArcGIS Online).

I have done that by creating the service schema manually (sending a JSON schema definition).

So then I looked into how ArcGIS Online does it and looks like they use a combination of /addItem (https://developers.arcgis.com/rest/users-groups-and-items/add-item/) and /publish (https://developers.arcgis.com/rest/users-groups-and-items/publish-item/) to achieve this.

Some time ago, I created this Postman collection to demo the whole workflow. I would be something like:

1. Check that the service doesn't already exist (REST call)
2. Create the item targetType=featureService (e.g., REST call)
3. Add the schema definition to the service (e.g., REST call creating a point layer)

You can also check the Define a new feature layer tutorial included in the Portal and data services guide.

Update: I just a blog article that explains the different approaches to create hosted feature services among other things.

I hope this helps!

You don't need to upload an fGDB first. Even if you do, you can delete the fGDB from AGOL in code.

Here's how I publish (overwrite) without uploading an fGDB:

        arcpy.mp.CreateWebLayerSDDraft(mp, sddraft_file, map_name, overwrite_existing_service=True)
        print(4*" " + f"Staging local Service Definition:  {sd_file}")
        arcpy.StageService_server(sddraft_file, sd_file)

        print(4*" " + f"Overwriting online service definition:  {sd_item.title}")
        sd_item.update(data=sd_file)
        print(4*" " + f"Publishing feature service")
        pub_params = {"editorTrackingInfo": {"enableEditorTracking": 'true', "preserveEditUsersAndTimestamps": 'true'}}
        fs = sd_item.publish(publish_parameters=pub_params, overwrite=True)

You should be able to tweak this slightly to publish a new service, rather than overwrite an existing one.

Note that instead of leaving a fGDB sitting in AGOL, this will leave a service definition sitting in AGOL. Again, you can delete this (in code) if you wish. However, that would mean you could no longer overwrite the feature service in-place.