Here is a guide that will help you in this situation:
If you look at the browser network, you can see the request made when you unlike:
DELETE /post_actions/<post_id>
The action_summary
IDs represent the actions on the post:
1: bookmark
2. like
3. flag off-topic
4. flag inappropriate
5. vote
6. flag notify user
7. flag notify moderator
8. flag spam
4 Likes