403 error in Claude

Despite having the Full Subscription, installed MCP into Claude correctly, and pasting the correct API key into the json file, a 403 error keeps appearing.

{
  `full_text_queries`: [
    {
      `field_name`: `document_title`,
      `search_term`: ``
    }
  ],
  `vector_search_term`: `books with most highlights`
}

Response
Request failed with status code 403