Mime Type / file extension for file inputs

Hi. I’m building an app using the Responses API where I need to pass files as input. We first upload the files using the Files API, with user_data purpose and the we reference them using file_id.

How relevant/important are the mime type and file extension for both APIs? I noticed that some extensions are rejected via the Files API (eg. .log). Also in the Responses API it seems to work sending a log file (.log, officially documented) even if the mime type is set as application/octet-stream (not mentioned as accepted)

Can the mime type be set to any value as long as the extension is accepted? Is the mime type relevant?