API to upload subtitle file

I am reviewing the API documents
https://www.lingq.com/apidocs/api-1.0.html#post-https---www.lingq.com-api-v2-language-lessons-

I am able to find this API
POST https://www.lingq.com/api/v2/ja/lessons/

However, this endpoint only allows me to specify the content as text.

When I upload subtitle via the website, the website can pick up the timestamp info as well. So I am trying to see if I can upload the subtitle file via the API.

Any suggestion?