@korina Hi, sorry but I don't understand how the post you suggested can help me. My code is the same as the tutorial but the error I mentioned in ther previous post occurs.
Here is my js code:

var options = {
    key: '**MY KEY**',
    verbose: true,
    lat: 50.4,
    lon: 14.3,
    zoom: 5,
};
windyInit(options, function (windyAPI) {
    vm.map = windyAPI;
    L.popup()
    .setLatLng([50.4, 14.3])
    .setContent('<p>Hello world!<br />This is a nice popup.</p>')
    .openOn(vm.map);
});

Hi,
I'm new here, I'm testing free api because the service seems to be very interesting but I want to be sure Windy will fit all my business requirements. I've just tryed to reproduce this tutorial https://api.windy.com/map-forecast/examples/hello-world but when I call openOn function an error occured: Uncaught TypeError: map.openPopup is not a function. I already use Leaflet map in another scenario into my website and I do not have this error. I'm able to open popup, add marker, layers and so on. Is this a problem related to free api key I'm using or there could be something I do wrong? Thanks