foreignId that is sent to the users endpoint, which does not already exist. If the user already exists, the user will be updated with the new properties and events.
If you wish to create a user without any properties, you can simply call the endpoint with the foreignId:
GET /v1/users endpoint. As this endpoint returns PII, you will need to use the private API key. You should not use this endpoint in your frontend code, as it will expose your private API key.