I am trying to send two pieces of data - a form and an array via AJAX to a Flask endpoint. My javascript with only sending the form is here:

$(document).on('click', '#submit_button', function(){
    let form_data = $('#form').serialize();
    let other_data = updateOtherData();

    req  = $.ajax({
        url : url_final,
        type : 'POST',
        data : form_data
    });
    req.done(function(data){
    //does some updates to page here
    });
});

And in my flask endpoint this works just fine with doing something like:

@app.route('/process_form', methods=['GET', 'POST'])
def process_form():
  form = MyForm()
  if request.method == 'POST' and form.validate_on_submit():
  #do something here
  return some_data_back

However, I would like to send other_data along with form_data. So I have tried:

$(document).on('click', '#submit_button', function(){
    let form_data = $('#form').serialize();
    let other_data = updateOtherData();

    req  = $.ajax({
        url : url_final,
        type : 'POST',
        data : {'form': form_data, 'other': JSON.stringify(other_data)}
    });
    req.done(function(data){
    //does some updates to page here
    });
});

And updated my endpoint to something like:

@app.route('/process_form', methods=['GET', 'POST'])
def process_form():
  form = MyForm()
  if request.method == 'POST':
      form = #Turn this back to a FlaskForm object
      other_data = #Just get this as a string
  if request.method == 'POST' and form.validate_on_submit():
      #do something here
  return some_data_back

I have tried a lot of different parts in the above where I cant get it to work. I have tried request.form, request.data, and request.get_json (in which I set contentType in ajax call).

I have looked at many similar questions such as: Get the data received in a Flask request and Get raw POST body in Python Flask regardless of Content-Type header which looked very promising, but everything kept coming across empty.