Request being Barred by CORS policy

I'm trying to mount my Front End using the Icinga API, but I'm constantly encountering the following error:

  

Access to XMLHttpRequest at   ' link '   from origin ' link ' has been blocked by CORS policy:   In 'Access-Control-Allow-Origin' header is present on the requested   resource.

I've tried everything, I've seen all the possible tutorials on the internet and I could not. But what makes me more curious is that I can make this same request for Postman without any difficulty.

Remembering that:

Now, my doubts focus on the following: How does Postman do this and if there is a possibility I can see the request that was made by Postman, so I can copy it.

$.ajax({
    url: "url",
    crossDomain: true,
    data: "",
    dataType: 'json',
    success: function (data) {
        console.log(data);
    },
    type: 'GET'
});