Get 400 error Cannot send package without approvals when eslClient.SendPackge()

Use the .NET sample code https://developer.esignlive.com/guides/feature-guides/document-extraction/ to generate eSign. The field name is [Client1.Capture1] with field type is 'Signature' in PDF file. But get error message Silanis.ESL.SDK.EslServerException: Could not send the package. Exception: The remote server returned an error: (400) Bad Request. HTTP POST on URI https://sandbox.e-signlive.com/api/packages/4sXpv6J-abrL0mKD3U3dJ0gfhIc=. Optional details: {"messageKey":"error.validation.sendPackage.noApprovals","message":"Cannot send package without approvals.","code":400,"name":"Validation Error"} ---> Silanis.ESL.SDK.EslServerException: The remote server returned an error: (400) Bad Request. HTTP POST on URI https://sandbox.e-signlive.com/api/packages/4sXpv6J-abrL0mKD3U3dJ0gfhIc=. Optional details: {"messageKey":"error.validation.sendPackage.noApprovals","message":"Cannot send package without approvals.","code":400,"name":"Validation Error"} ---> System.Net.WebException: The remote server returned an error: (400) Bad Request. at System.Net.HttpWebRequest.GetResponse() at Silanis.ESL.SDK.Internal.HttpMethods.PostHttp(String apiToken, String path, Byte[] content, IDictionary`2 headers) --- End of inner exception stack trace --- at Silanis.ESL.SDK.Internal.HttpMethods.PostHttp(String apiToken, String path, Byte[] content, IDictionary`2 headers) at Silanis.ESL.SDK.RestClient.Post(String path, String jsonPayload) at Silanis.ESL.SDK.Services.PackageService.SendPackage(PackageId packageId) --- End of inner exception stack trace --- at Silanis.ESL.SDK.Services.PackageService.SendPackage(PackageId packageId) at eSignDemo.Controllers.ValuesController.Get() in C:\Users\xxie\source\repos\Projects\eSignDemo\eSignDemo\Controllers\ValuesController.cs:line 122 my code is EslClient eslClient = new EslClient(key, url); DocumentPackage superDuperPackage = PackageBuilder.NewPackageNamed("Test Document Extraction") .WithSettings(DocumentPackageSettingsBuilder.NewDocumentPackageSettings()) .WithSigner(SignerBuilder.NewSignerWithEmail("[email protected]") .WithFirstName("John") .WithLastName("Smith") .WithCustomId("Client1") ) .WithSigner(SignerBuilder.NewSignerWithEmail("[email protected]") .WithFirstName("Michael") .WithLastName("Williams") .WithCustomId("MawerIC1") ) .WithDocument(DocumentBuilder.NewDocumentNamed(DOCUMENT1_NAME) .FromStream(ms, DocumentType.PDF) .EnableExtraction() ) .Build(); PackageId packageId; try { packageId = eslClient.CreatePackageOneStep(superDuperPackage); eslClient.SendPackage(packageId); } catch (Exception e) { return BadRequest(e.ToString()); }