Cannot delete attachment from a list item from a sharepoint online app

I get a success message after running the following displayed below. However, when I go and verify the list item the file is still there. If I try the client side of this code, the file gets deleted, I'm not sure if I'm missing something.

function initialize(){ var scriptbase = hostweburl + "/_layouts/15/";

$.getScript(scriptbase + "SP.RequestExecutor.js", execCrossDomainRequest);

function execCrossDomainRequest() {

var executor = new SP.RequestExecutor(appweburl);

var digest = $("#__REQUESTDIGEST").val();

        executor.executeAsync({              
            url: appweburl + "/_api/SP.AppContextSite(@target)/web/lists/getbytitle('TestList')/getItemById(1)/AttachmentFiles/getbyFileName('test - -File.xlsx')?@target='" +  hostweburl + "'",    
            type: "POST",
            headers: {
                "Accept": "application/json;odata=verbose",
                "X-Http-Method": "DELETE",
                "X-RequestDigest": $("#__REQUESTDIGEST").val()
            },             
            success: function (data) {  
                alert("success: " + JSON.stringify(data));  
            },  
            error: function (err) {  
                alert("error: " + JSON.stringify(err));  
            }    
        });                              

} }