AJAX call using admin-ajax URL is returning 400 bad request

I am attempting to create an AJAX call to pass custom taxonomy into my WP_Query but I am getting 400 (Bad Request). I believe my data array is built correctly so I am not sure what's causing it. Does anything look off here? Is there a way for me to get a more detailed error of why it is returning error 400?

$.ajax({
    type:'POST',
    url:ajaxUrl,
    data: {
        taxonomy: 'products',
        slug: 'shirts'
    },
    beforeSend:function(xhr){

    },
    success:function(data){
      $('#response').html(data); // insert data
    }
});

I console logged ajaxUrl and I am getting the correct path to admin-ajax.php so I know that's not the issue. I think it has to have something to do with data.