Rest API filtering

My posts collections includes tags as follows

 {
      name: 'tags',
      type: 'relationship',
      relationTo: 'tags',
      hasMany: true,
    },

I want to be able to filter the response by tag name. I also want to place a limit of 6 so I don't break my pagination, etc.

Given a tag of "Guides", shouldn't I be able to filter my posts using

https://domain.com/api/posts?where[tags][equals]=Guides&limit=6&page=1

The above url params don't work. I've attached a screenshot of the api response.

I'm using this url based on my interpretation of the following documentation -

What am I doing wrong?