Beginner need help JSON

Hello, I normally speak German and have translated this.

I am just starting with MIT App Inventor.
I need to implement something that queries a web API.
But I just don't know which blocks to use.
I have a button to trigger the action and two text fields to display the results.
I have received the code, but I don’t know how to modify it.
Can someone help me with this? I've been trying for hours.
Thank you.

Here is the code:

function getData() {
    var requestObj = {};
    requestObj.getvars = [ ];
    var toget = { "var": "(A:PLANE ALTITUDE, Feet)", "value": 0 };
    requestObj.getvars.push(toget);
    toget = { "var": "(A:GROUND VELOCITY, Knots)", "value": 0 };
    requestObj.getvars.push(toget);
    
    var xhttp = new XMLHttpRequest();
    xhttp.addEventListener("load", dataRequestListener);
    xhttp.open("GET", AAO_URL + "?json=" + JSON.stringify(requestObj));
    xhttp.send();
    }

    function dataRequestListener() {
        var commObj = JSON.parse(this.responseText);
        var myalt = commObj.getvars[0].value;
        var myspeed = commObj.getvars[1].value;
    }

Is there a link to the API documentation?
That code snippet does not help very much...

Taifun

The link to the API is:

starting from page 149 / 20. Web API.
I want to retrieve a value, not send one.
Unfortunately, I don't understand the whole thing well enough.
Thank you for reviewing it.

Well, I have no idea...
Try to find an example what you want to do in another language... are there several options available?

Maybe their forum can help?
https://www.avsim.com/forums/forum/906-axisandohs-support/

Taifun