<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:web="http://api.channeladvisor.com/webservices/">
   <soapenv:Header>
      <web:APICredentials>
         <web:DeveloperKey>XXX</web:DeveloperKey>
         <web:Password>XXX</web:Password>
      </web:APICredentials>
   </soapenv:Header>
   <soapenv:Body>
      <web:AddMarketplaceAdForSkuList>
         <web:accountID>XXX</web:accountID>
         <web:skuList>
            <web:MarketplaceAdSkuRequest>
               <web:Sku>SKU0001</web:Sku>
               <web:AdTitleOverride>Ad Title for SKU0001</web:AdTitleOverride>
            </web:MarketplaceAdSkuRequest>
            <web:MarketplaceAdSkuRequest>
               <web:Sku>SKU0002</web:Sku>
               <web:AdTitleOverride></web:AdTitleOverride>
            </web:MarketplaceAdSkuRequest>
            <web:MarketplaceAdSkuRequest>
               <web:Sku>SKU0003</web:Sku>
               <web:AdTitleOverride>Ad Title for SKU0003</web:AdTitleOverride>
            </web:MarketplaceAdSkuRequest>
            <web:MarketplaceAdSkuRequest>
               <web:Sku>SKU0004</web:Sku>
               <web:AdTitleOverride></web:AdTitleOverride>
            </web:MarketplaceAdSkuRequest>
         </web:skuList>
         <web:postingTemplate>My Favorite Posting Template</web:postingTemplate>
         <web:adTemplate>My Favorite Ad Template</web:adTemplate>
         <web:schedule></web:schedule>
         <web:flagStyle>NoFlag</web:flagStyle>
         <web:flagDescription></web:flagDescription>
         <web:primaryCategory></web:primaryCategory>
         <web:secondaryCategory></web:secondaryCategory>
         <web:primaryStoreCategory></web:primaryStoreCategory>
         <web:secondaryStoreCategory></web:secondaryStoreCategory>
      </web:AddMarketplaceAdForSkuList>
   </soapenv:Body>
</soapenv:Envelope>

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <soap:Body>
      <AddMarketplaceAdForSkuListResponse xmlns="http://api.channeladvisor.com/webservices/">
         <AddMarketplaceAdForSkuListResult>
            <Status>Success</Status>
            <MessageCode>0</MessageCode>
            <Message></Message>
            <ResultData>
               <MarketplaceAdSkuResponse>
                  <Sku>SKU0001</Sku>
                  <MarketplaceAdID>1234567</MarketplaceAdID>
                  <ErrorMessage></ErrorMessage>
               </MarketplaceAdSkuResponse>
               <MarketplaceAdSkuResponse>
                  <Sku>SKU0002</Sku>
                  <MarketplaceAdID>1234568</MarketplaceAdID>
                  <ErrorMessage></ErrorMessage>
               </MarketplaceAdSkuResponse>
               <MarketplaceAdSkuResponse>
                  <Sku>SKU0003</Sku>
                  <MarketplaceAdID>1234569</MarketplaceAdID>
                  <ErrorMessage></ErrorMessage>
               </MarketplaceAdSkuResponse>
               <MarketplaceAdSkuResponse>
                  <Sku>SKU0004</Sku>
                  <MarketplaceAdID>1234570</MarketplaceAdID>
                  <ErrorMessage></ErrorMessage>
               </MarketplaceAdSkuResponse>
            </ResultData>
         </AddMarketplaceAdForSkuListResult>
      </AddMarketplaceAdForSkuListResponse>
   </soap:Body>
</soap:Envelope>
 

// Create your credentials
CA_API_MarketplaceAdSvc.APICredentials cred = new CA_API_MarketplaceAdSvc.APICredentials();
cred.DeveloperKey = "dev-key-guid";
cred.Password = "pwd";// Create the Web Service and attach the credentials
CA_API_MarketplaceAdSvc.MarketplaceAdService svc = new CA_API_MarketplaceAdSvc.MarketplaceAdService();
svc.APICredentialsValue = cred;

// Create the MarketplaceAd
List<CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest> skuList = new List<CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest>();
CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest sku1 = new CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest();
sku1.Sku = "SKU0001";
sku1.AdTitleOverride = "Ad Title for SKU0001";
skuList.Add(sku1);

CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest sku2 = new CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest();
sku2.Sku = "SKU0002";
skuList.Add(sku2);

CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest sku3 = new CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest();
sku3.Sku = "SKU0003";
sku3.AdTitleOverride = "Ad Title for SKU0003";
skuList.Add(sku3);

CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest sku4 = new CA_API_MarketplaceAdSvc.MarketplaceAdSkuRequest();
sku4.Sku = "SKU0004";
skuList.Add(sku4);

// Now just call the method
CA_API_MarketplaceAdSvc.APIResultOfArrayOfMarketplaceAdSkuResponse result =
     svc.AddMarketplaceAdForSkuList(
          "acct-guid",
          skuList.ToArray(),
          "My Favorite Posting Template",
          "My Favorite Ad Template",
          null,
          CA_API_MarketplaceAdSvc.FlagType.NoFlag,
          null,
          null,
          null,
          null,
          null
     );