Making HTTP POST Requests from Proxy App to Backend result in Bad Request 400 Errors

[aidendev]

Last year,  I had a proxy application that allowed me to pull data of the signed in user via ajax, and allow them to submit their updated profile data via ajax as well.

I have been able to perform HTTP GET requests successfully, but not HTTP POST requests (results in HTTP 400 Bad Request Error). 

To be clear, I am not using a theme app extension - I have a button that triggers an ajax call and my goal is to be able to send the data to my backend method. This is the setup I have:

 $.ajax({
     type: 'POST',
     url: '/apps/member-area?handler=UpdateCollectorInfo',
     contentType: 'application/json',
     data: JSON.stringify(formData),
     headers: {
         'X-Shopify-Access-Token': accessToken,
         'RequestVerificationToken': antiForgeryToken
         
     },
     dataType: 'json',
     beforeSend: function (jqXHR, settings) {
         console.log('Request URL:', settings.url);
         console.log('Request Type:', settings.type);
  
     },
     xhrFields: {
         withCredentials: true
     },
     success: function (response) {
         if (response.success) {
             $('#UserFeedbackMessage').text(response.message).css('color', 'green').show();
         } else {
             $('#UserFeedbackMessage').text(response.message).css('color', 'red').show();
         }
     },
     error: function (xhr, status, error) {
         console.error("Error updating collector info:", error);
         console.log("XHR:", xhr);
         console.log("Status:", status);
         console.log("Response Text:", xhr.responseText);
         $('#UserFeedbackMessage').text("An error occurred while updating your profile.").css('color', 'red').show();
     },
     complete: function (jqXHR, status) {
         console.log('Complete Response Headers:', jqXHR.getAllResponseHeaders());
     }
 });

 I have been wrestling with this problem all week, and have thoroughly looked through docs, the forum, stackedoverflow, etc... any help,  would be greatly appreciated 😅