It seems like the issue might be related to how the fetch API is used or possibly with the response handling. Here are a few things to check and possible fixes:

1. Network Monitoring:
   If your Network Monitor doesn’t show the /CheckItem request, it means the request isn’t reaching the server. This could be due to:

• An incorrect or unreachable URL.
• The browser blocking the request due to CORS issues (Cross-Origin Resource Sharing).
• The fetch function failing silently due to a network error or misconfigured request headers.

2. ensure fetch is properly handling errors:
   Wrap the fetch call in a try-catch block to catch any errors. fetch won’t throw an error on HTTP errors (like 404 or 500), but it will throw an error if the network request fails, so it’s good to check for this.

Here is a modified version of your code with error handling:

javascript
async function postAjaxWithFetch(url, data) {
try {
// if data is a string, use it as-is. If it is an object, generate a form-encoded string from it.
const params = typeof data === ‘string’ ? data : Object.keys(data)
.map(k => ${encodeURIComponent(k)}=${encodeURIComponent(data[k])})
.join(‘&’);

    const request1 = new Request(url, {
        method: "POST",
        body: params,
        headers: {
            'X-Requested-With': 'XMLHttpRequest',
            'Content-Type': 'application/x-www-form-urlencoded',
        },
    });

    // Use fetch to make the request and wait for the response
    const response1 = await fetch(request1);

    // If fetch was successful, but the response is not ok (e.g. 404 or 500), throw an error
    if (!response1.ok) {
        throw new Error(`HTTP error! Status: ${response1.status}`);
    }

    // Convert response to JSON or text depending on your response format
    const data = await response1.json();  // Or response1.text() if not using JSON
    console.log(data);
    return data;
} catch (error) {
    console.error("Error in postAjaxWithFetch:", error);
    alert("Error during POST request: " + error.message);
    return null;  // Return null or some default value in case of error
}

}

Check the Response Type:
If the server response is not JSON, and you’re trying to parse it as JSON, it can cause issues. If your response is plain text, adjust your code accordingly:

javascript
const data = await response1.text(); // If your response is not JSON

4. CORS and Server-Side Considerations:

• CORS Issues: Ensure that your server is allowing the browser to make cross-origin requests. If the server is on a different domain than your client, you’ll need to configure CORS on the server to allow the POST request.

• Server Logs: Check your server logs to ensure it’s receiving the request properly. If the server doesn’t log anything, it may mean the request isn’t reaching the server at all.

Double-Check URL:
Ensure that the /CheckItem endpoint is correct. It might be an issue with the relative URL or incorrect routing on the server.

6. Debugging Tips

• Log the request1 object before the fetch call to verify that the request is being created properly.
• Use console.log statements throughout your async function to track its flow.

If none of these suggestions work, please provide more details about the server and network setup so we can investigate further!