Subscribed calendars not shown on my device, but they can be opened manually [iOS 14.4.2]

I am trying to write a PHP service to make calendars from some data. Anyway, the example it returns (it is static during the test) shows up normally when trying to get it by http://my_domain.com/ics.php or just to download response as an .ics file (location, URL, description, alert fields have been shown properly, I can save it on my device or CalDAV/Cloud server), so the iCS syntax is OK. But when I try to subscribe to it through webcal://my_domain.com/ics.php, its events do not show up on my Calendar timeline (although I can still see it in the "Calendars" sections and even "refresh" it). When refreshing it, the events still can't be seen, but the server notices the request to my_domain.com/ics.php. I tried: - Rebooting the device & server - Making a static .ics file and subscribing to it - Adding response headers like Content-type: text/calendar and Content-disposition: attachment; filename=index.ics - Disabling iCloud & Google Calendars accounts on the device - Generating another event in the calendar And nothing above helped. The subscribition works on Microsoft Outlook, Mozilla Thunderbird on Windows 10 device. On my i-device there was another public subscribed calendar, but it also did not worked. The example of generated ICS can be watched here . What should I change to make it subscribed and shown properly? I will appreciate any provided help! Added: now when accessing through webcal:// safari responses that "Can't opent the page because it is invalid"