Safari Push Notifications can't be allowed

I'm trying to implement safari push notifications on my site using this guide https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/NotificationProgrammingGuideForWebsites/PushNotifications/PushNotifications.html

There is a button on the site and the following JS code:

window.onload = function() {                                                                                               
  var p = document.getElementById('subscribe');                                                                            
  p.onclick = function() {                                                                                                 
    // Ensure that the user can receive Safari Push Notifications.                                                         
    if ('safari' in window && 'pushNotification' in window.safari) {                                                       
      var permissionData = window.safari.pushNotification.permission('MY_REAL_WEBSITE_PUSH_ID');       
      checkRemotePermission(permissionData);                                                                               
    }                                                                                                                      
  };                                                                                                                       

  var checkRemotePermission = function(permissionData) {                                                                   
    console.log(permissionData);                                                                                           
    if (permissionData.permission === 'default') {                                                                         
      // This is a new web service URL and its validity is unknown.                                                        
      window.safari.pushNotification.requestPermission(                                                                    
        'MY_REAL_WEBSERVICE_URL', // The web service URL.                                             
        'MY_REAL_WEBSITE_PUSH_ID',     // The Website Push ID.                                         
        {}, // Data that you choose to send to your server to help you identify the user.                                  
        checkRemotePermission         // The callback function.                                                            
      );                                                                                                                   
    }                                                                                                                      
    else if (permissionData.permission === 'denied') {                                                                     
      // The user said no.                                                                                                 
    }                                                                                                                      
    else if (permissionData.permission === 'granted') {                                                                    
      // The web service URL is a valid push provider, and the user said yes.                                              
      // permissionData.deviceToken is now available to use.                                                               
    }                                                                                                                      
  };                                                                                                                       
}

As a result when I press the button I get request permission.

When I disallow notifications all works as expected: console.log(permissionData); shows permissionData.permission equals denied and I can see site as denied at Safari's Preferences -> Notifications section.

But when I allow notification nothing happens. It seems checkRemotePermission doesn't fire as window.safari.pushNotification.requestPermission's callback.

Any thoughts?