I have a SurfaceController that performs a Get method. When I attempt to access the current page using this.CurrentPage, I get the following error

Cannot find the Umbraco route definition in the route values, the request must be made in the context of an Umbraco request

Why is my controller not able to see the current page?

{ using System; using System.Threading.Tasks; using System.Web.Mvc; ... using Umbraco.Web.Mvc;

public class BenefitStatementPdfSurfaceController : SurfaceController
{
    private readonly SelfServiceApiHttpClient _apiClient;

    public MySurfaceController(SelfServiceApiHttpClient apiClient)
    {
        _apiClient = apiClient;
    }

    [ActionName("MemberPdf")]
    [HttpGet]
    [Authorize]
    public async Task<ActionResult> MemberPdfAsync(int memberNumber, int selectedYear)
    {
        var content = await _apiClient
                                .MemberPdfAsync(memberNumber, selectedYear)
                                .ConfigureAwait(false);
        if (content.HasPdf)
        {
                return this.File(content.Pdf, "application/pdf", $"Statement{selectedYear}_{DateTime.Now:yyyyMMdd}_{DateTime.Now:HHmmss}.pdf");
        }

        var nodeId = this.CurrentPage.Id; ------ERRORS HERE
       ...
    }
}

}