How to match value sent by ajax call in a Rails controller and display an error message?

<%= form_for(@mymodel, remote: true, html: { id: 'match_form' }) do |f| %>
        <!-- I need to check if @mymodel.match_id matches the value generated by a controller function -->
   <%= f.submit 'Save', class: 'btn btn-primary', id: 'match_submit', style: "width:38px;padding:0px" %> 
   <%= button_tag 'Cancel', class: 'btn btn-secondary', id: 'match_cancel', style: "width:52px;padding:0px" %>
<% end%>
<script type='text/javascript'>
    $(function() {
      $(document).on("click", "#match_submit", function(event){
        $.ajax('my_controller_method', {
          type: 'GET',
          dataType: 'script',
          data: {
            mid: $("#").val(),  // how do I pass @mymodel.match_id here?
          },
          error: function(jqXHR, textStatus, errorThrown) {
          return console.log("AJAX Error: " + textStatus);
        }
      });      
    });
  </script>

I have a form as shown above.

1. How do I pass @mymodel.match_id in the ajax call above?
2. In my controller function, I would like to check if passed match_id is a certain value; if not, I would like to display a modal with an error message and just an Ok button. How can I achieve this?
   < > a) Should I return the correct value from controller function and check the same in my javascript code above and show a javascript alert?
   < >< > i) If yes, then how can I return a number from a controller function to my JavaScript invoking function?
   or
   < > b) would I be able to render a bootstrap modal with an Ok button in my controller itself?

UPDATE 1:

I tried this to pass match_id and id from mymodel to the ajax call but it did not work:

$(document).on("click", "#match_submit", function(event){
      alert ("match id changed!");
      alert($("#match_form").data('id'));
      alert($("#match_form").data('match_id'));

      $.ajax('cpl_evaluate_match_id', {
        type: 'GET',
        dataType: 'script',
        data: {
          debit_id: $("#match_form").data('id'),
          match_id: $("#match_form").data('match_id')
        },
        error: function(jqXHR, textStatus, errorThrown) {
        return console.log("AJAX Error: " + textStatus);
      }
      });      
    });

The alerts to print id and match_id print undefined in the alert messages.

UPDATE 2:

I tried this to return a number from my controller function but this doesn't seem to work either:

  def evaluate_match_id
    puts params[:debit_id]
    puts params[:match_id]

    return 1
  end

the puts above turn up blank

    $(document).on("click", "#match_submit", function(event){
      alert ("match id changed!");
      alert($("#match_form").data('id'));
      alert($("#match_form").data('match_id'));

      $.ajax('cpl_evaluate_match_id', {
        type: 'GET',
        dataType: 'script',
        data: {
          debit_id: $("#match_form").data('id'),
          match_id: $("#match_form").data('match_id')
        },
        success: function(result){
                    if(result){ // yes or no? 1 or 0, it's the return coming from your controller
            alert('true');
            alert(result);
          }
          else{
            alert('error');
            alert(result);
          }
        },
        error: function(jqXHR, textStatus, errorThrown) {
        return console.log("AJAX Error: " + textStatus);
      }
      });      
    });

The value of result in the success: block in the JavaScript code above comes up as undefined (my controller function blindly returns the number 1 which I was expecting to be the value of result here)