使用'categories'参数总会产生WordPress Rest API错误，“rest_post_invalid_page_number”？

Question

I am working on a web app in PHP that must display recent blog posts of a specific category from a separate WordPress site. We are accessing these posts via the REST API. When I use the categories argument, I get a 400 error. Without the categories argument (and with all other endpoints I've tried), I get a successful response.

• The posts are being requested from a site running WordPress 5.2.1.
• For now, I am just accessing the endpoints via my browser, and viewing the JSON returned there.
• I am using the endpoint: https://itherapy.com/wp-json/wp/v2/posts?categories=60.
• There are 43 published / public posts in the posts category with the id of 60.
• Even if I specify the additional arguments of per_page and page (for example, like https://itherapy.com/wp-json/wp/v2/posts?categories=60&per_page=1&page=1), I get the same error. By removing the categories argument (like this: https://itherapy.com/wp-json/wp/v2/posts?per_page=2&page=2), the other arguments work (ie, I get 2 posts, offset by 2 posts), but this is for ALL posts. That is expected, but why might the categories argument be breaking my request?

I can submit similar requests to the WordPress Rest API demo site, like so: https://demo.wp-api.org/wp-json/wp/v2/posts?categories=11, and all of the posts from category 11 are returned. the same request made from my domain fails.

The endpoint I am trying to access data from is:

https://itherapy.com/wp-json/wp/v2/posts?categories=60

The error message I am getting back is:

{
  "code": "rest_post_invalid_page_number",
  "message": "The page number requested is larger than the number of pages available.",
  "data": {
    "status": 400
  }
}