When using this trigger you will see the option is "Liked tweet by a specific user":
There is not an option for "triggered when anybody likes one of your tweets", which I would imagine is the more popular use case.
Then you get to customization and a specific user is a compulsory field:
Quick hack: Just insert "@" into that field and you will get all your liked tweets
@ChrisP - thanks for posting!
One other bug seems to be that the “URL” field seems to insert “@” in place of the username.
Best thing to do is report that to Zapier. You can open a ticket here: https://zapier.com/app/contact-us