Getting 403 error in non-public API but not blocked from domain

I hope everything is good with you!

I created a tool in C# that would run every day and was able to fetch me the prices of all the products in certain categories of my choice from the Cex website (uk.webuy.com). I used this tool to keep a price history for the products but one day, as the tool was executing, it started getting a 403 error. I haven't been able to diagnose why this is happening since other end-points from this domain work completely fine.

Here is the code I have been using for the last 6 months for the request:

public static List<Box> GetCategoryProducts(List<int> largeCategoriesList)        {            List<Box> boxes = new List<Box>();            foreach (int categoryId in largeCategoriesList)            {                int currentCategoryProducts = 0;                int firstRecord = 1;                int count = 50;                int totalRecords = 0;                int minDelay = 3;                int maxDelay = 6;                int retryDelay = 10; // Retry after 10 seconds if response isn't successful                bool hadError = false;                int retryCount = 0;                do                {                    try                    {                        string weBuyAPILink = $"https://wss2.cex.uk.webuy.io/v3/boxes?firstRecord={firstRecord}&count=50&sortBy=relevance&sortOrder=desc&categoryIds=[{categoryId}]";                        var client = new RestClient(weBuyAPILink);                        client.Timeout = -1;                        var request = new RestRequest(Method.GET);                        List<KeyValuePair<string, string>> headerList = new List<KeyValuePair<string, string>>()                        {                            new KeyValuePair<string, string>("Accept", "application/json, text/plain, */*"),                            new KeyValuePair<string, string>("Refer", "https://uk.webuy.com"),                            new KeyValuePair<string, string>("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/121.0.0.0 Safari/537.36"),                            new KeyValuePair<string, string>("Origin", "https://uk.webuy.com"),                            new KeyValuePair<string, string>("Accept-Encoding","gzip, deflate, br")                        };                        request.AddHeaders(headerList);                        IRestResponse response = client.Execute(request);                        if (!response.IsSuccessful)                        {                            Logger.Error($"Request response encountered an error! Error details: {response.StatusCode}");                            hadError = true;                            Thread.Sleep(retryDelay * 1000); // Retry after 10 seconds                            retryCount++;                        }                        else                        {                            //PROCESS RESPONSE                            //.......                            //.......                            hadError = false;                            var random = new Random();                            var delay = random.Next(minDelay * 1000, maxDelay * 1000);                            Logger.Info($"Waiting {delay / 1000} seconds before next request...");                            Thread.Sleep(delay);                        }                    }                    catch (Exception ex)                    {                        Logger.Fatal(ex, "Fatal error processing category list!");                        // Handle fatal error as needed                        hadError = true;                    }                } while ((currentCategoryProducts < totalRecords || totalRecords == 0) && !hadError && retryCount < 3); // Retry only 3 times                if (hadError)                {                    Console.WriteLine("Unable to get price info");                }            }            return boxes;        }

Trying to access the URL on a browser will give a Cloudflare page saying that I have been blocked and that I can no longer access webuy.io, but, for example, accessing the product detailendpoint that gives me only the details from a specific product, works fine.

Can someone point me in the right direction? I've been looking at Cloudflare bypasses but I haven't invested a lot of time in them because I think that won't solve my issue.

I looked into this GitHub repo when building my tool as it had some insightful information about the API.

I tried changing some request headers, tried using a VPN, and also tried using ScraperAPI and ScrapeOps to fetch me the information without getting the 403 error but to no avail.