Why aren't tags and categories added in post request to WP Rest API

I’m using V2.0 and trying to create a post using the /posts endpoint.

Here’s the payload being sent with my request:

var payload =
   {
     title : "some title",
     format : "link",
     tags: ["tag1", "tag2"],
     categories: ["newsletter"],
     content: "http://someurl.com",
     status: "publish"
   };

The posts are successfully being created and all other fields are added except for the category and tags.

I see that both of them are supposed to take an array of strings. What am I missing here?

Also, I’ve tried adding both categories and tags that already exist on the site, and brand new ones. both don’t work.