Microsoft Graph - copilot/search how to get nextLink

Hi, I'm having issues getting all the result back from from the search. I'm using "Graph Explorer" to try out /beta/copilot/search, using the request:

{
  "query": "test",
  "pageSize": 10,
  "dataSources": {
    "oneDrive": {
      "resourceMetadataNames": [
        "title",
        "author"
      ]
    }
  }
}

I'm getting the response:

{
    "searchHits": [
        {
            "webUrl": "https://xxx.sharepoint.com/sites/xxxx/Documents/AM%20Test.docx",
            "resourceType": "listItem",
            "preview": "This is a Template Document  This field, AM <c0>Test</c0>,comes from a workflow",
            "resourceMetadata": {
                "title": "AM Test",
                "author": "Andrew Morgan"
            }
        },
        {
            "webUrl": "https://xxx.sharepoint.com/sites/xxxx/Documents/Test%20project.docx",
            "resourceType": "listItem",
            "preview": "This is a Template Document. This field, Test project,comes from a workflow",
            "resourceMetadata": {
                "title": "Test project",
                "author": "Andrew Morgan"
            }
        },
        {
            "webUrl": "https://xxx.sharepoint.com/sites/xxxx/Documents/Presentation%20File.pptx",
            "resourceType": "listItem",
            "preview": "This is a test",
            "resourceMetadata": {
                "title": "Presentation File.pptx",
                "author": "Andrew Morgan"
            }
        },
        {
            "webUrl": "https://xxx.sharepoint.com/sites/xxxx/Documents/Test%20project.xlsx",
            "resourceType": "listItem",
            "preview": "Input Key notes",
            "resourceMetadata": {
                "title": "Test project",
                "author": "Andrew Morgan"
            }
        },
        {
            "webUrl": "https://xxx.sharepoint.com/sites/xxxx/Documents/Test%202.docx",
            "resourceType": "listItem",
            "preview": "Hello Everyone,\r\nWelcome to …......\r\n",
            "resourceMetadata": {
                "title": "Test 2",
                "author": "Andrew Morgan"
            }
        }
    ],
    "totalCount": 1668
}

What I dont understand is the totalcount is 1668. Buit it doesnt seem to make any difference what I set pageSize to in the request I only ever get back 5 results and also I was expecting "@odata.nextLink" to get the next page of results. 

Can anyone shed any light on what i'm doing wrong or is it that i'm not understanding the document here:

https://learn.microsoft.com/en-us/microsoft-365/copilot/extensibility/api/ai-services/search/copilotroot-search

Thanks in advance!