Promise not returning value of request

I have this promise:

function getAPI(token)
{
return new Promise((resolve, reject) => {
    console.log("Request API");
    GM_xmlhttpRequest({
        method: "GET",
        url: "URL"+token,
        onload: function(response) {
            console.log(response.responseText);
            if( response.responseText == "NOT_ANSWER" || response.responseText.indexOf("ERRO") > -1 ){
                console.log(response.responseText + " - Calling Myself in 5 Seconds");
                setTimeout(function(){
                    getAPI(token);
                },5000);
            }
            else{
                console.log('Call API - Giving Result');
                resolve(response.responseText.split("_")[1]);
            }
        }
    });
});

}

I call it inside of itself when the answer is not what I want, cannot be less than 5 seconds though.

Then I do this in the main function:

setTimeout( function(){
                getAPI(token).then((key) => {
                    console.log(key);
                    doSomethingWithKey;
                    setTimeout( function(){
                        loop();
                    },1000);
                }).catch(() => {
                    console.log('Error na api - reload page!');
                    location.reload();
                });
            },25000);

But I noticed that when getAPI calls itself cause answer is not what i want, the '.then' in the main function never executes and my code hangs there. How can I fix it? I don't understand much of promises but I can't see why it hangs ...

I call it inside of itself when the answer is not what i want,

and then you don't call resolve of the promise which you had returned from the top getAPI call, so the promise never settles and your then callback never gets any result.

You should promisify your asynchronous functions GM_xmlhttpRequest and setTimeout on the lowest level, and then only chain your promises. By returning the result of the recursive call from a then callback, the resulting promise will resolve with the same result:

function xhrAsync(url) {
    return new Promise((resolve, reject) => {
        GM_xmlhttpRequest({
            method: "GET",
            url: url,
            onload: resolve
        });
    });
}
function delayAsync(time) {
    return new Promise(resolve => {
        setTimeout(resolve, time);
    });
}
function getAPI(token) {
    console.log("Request API");
    return xhrAsync("URL"+token).then(response => {
//  ^^^^^^                       ^^^^
        console.log(response.responseText);
        if (response.responseText == "NOT_ANSWER" || response.responseText.includes("ERRO")) {
            console.log(response.responseText + " - Calling Myself in 5 Seconds");
            return delayAsync(5000).then(() => {
//          ^^^^^^                  ^^^^
                return getAPI(token);
//              ^^^^^^
            });
        } else {
            console.log('Call API - Giving Result');
            return response.responseText.split("_")[1];
        }
    });
}