get responseText with Freemarker

Hello.

I have an endpoint that spits out a simple number as html.

I can use Ajax to get that number, but how do I get it in FM?

This works fine, for JS, but how do I get the variable returned as a FM variable, instead?

$.ajax({
	url: '/spotify/plugins/custom/spotify/spotify/my_custom_endpoint',
	error: function() {
		console.log('error')
	},
	success: function(responseText) {
		console.log(responseText)
   },
   type: 'GET'
});

I tried several http client response variants, but no success.