对原问题的评论是正确的，因为应该使用GraphQL变量。此外，它应该是使用async/await的异步代码。
但是，无论如何，即使使用Flurl，检索和处理分页的GraphQL结果仍然是一件真实的的痛苦的事情...
因此，我发布了FlurlGraphQL库（Flurl的扩展），它大大简化了GraphQL和Flurl的使用。
使用FlurlGraphQL，原始问题可以实现为：

//You don't have to work with the raw Json as it's alot more work/code 
//and the Library will greatly simplify this with a model such as 
//(educated guesses on data types, etc.)...
public class Product {
    public string Id {get; set;}
    public string Name {get; set;}
    public ProductBrand Brand {get; set;} //Define the Branch class also...
    public ProductPrices Prices  {get; set;} //Define the Prices class also...
    public ProductTags Tags {get; set;} //Define the Tags class also...
    public ProductBarcodes Barcodes {get; set;} //Define the Barcode class also...
    public decimal LastCost {get; set;}
    public decimal Cost {get; set;}
    public int CaseQuantity {get; set;}
    public string Image {get; set;}
}

var flurlGraphQL = await flurlAutUrl
    .WithGraphQLQuery(@"
        query ($first: Int, $after: String) {
            products(first: $first, after: $after) {
                totalCount
                edges {
                    node {
                        id
                        name
                        brand {
                            name
                        }
                        prices {
                            quantity
                            price
                        }
                        tags {
                            name
                        }
                        barcodes {
                            code
                        }
                        lastCost
                        cost
                        caseQuantity
                        image
                    }
                    cursor
                }
                pageInfo {
                    endCursor
                    hasNextPage
                }
            }
        }
    ");
    
//Get the First Page (we do not specify any value for $after)
var firstPageResults = flurlGraphQL
    .SetGraphQLVariables(new { first = 100 });
    .PostGraphQLQueryAsync()
    .ReceiveGraphQLConnectionResults<Product>();

//The Library makes getting the various Paging details 
//significantly easier...
var endCursor = firstPageResults.PageInfo.EndCursor;
    
//Get the Second Page using the End Cursor of the first, and this time 
//only retrieve 50 (per original question)...
var secondPageResults = flurlGraphQL
    .SetGraphQLVariables(new { first = 50, after = endCursor });
    .PostGraphQLQueryAsync()
    .ReceiveGraphQLConnectionResults<Product>();

foreach(var result in secondPageResults)
{
    //...process your results...
}

但如果您只想枚举页面并获取数据，这实际上更容易：

//Using the same initialized Flurl GraphQL query above we could async
//stream/enumerate all the pages...
var pagesAsyncEnumerable = flurlGraphQL
    .SetGraphQLVariables(new { first = 100 });
    .PostGraphQLQueryAsync()
    .ReceiveGraphQLConnectionPagesAsyncEnumerable<Product>();
        
await foreach (var page in pagesAsyncEnumerable)
{
    //...Process each page as a stream of Async Enumerable pages...
    //NOTE: The library has APIs to get ALL pages in a single blocking 
    //       request or get them in an IEnumerable too...
}