webcal:// protocol - creating ical reminders on Chrome iOS - hide subscribed URL from prompt?

I have a button on a website that adds a calendar event on click. I am using ics.js for most browsers, but a different solution on Safari on iOS, and with Chrome browser on iOS I have had to implement a webcal:// solution.

On click, URL opened is webcal://mysite.com?calreminder=[title]&time=[time]

Then server side we generate this output:

function reminder_output()
{
    if (isset($_GET['calreminder'])) {
        $title = $_GET['calreminder'];
        $time = $_GET['time'];

        $now = new DateTime();
        $start = new DateTime('tomorrow ' . $time);
        // event duration is 10 minutes
        $duration = new DateInterval('PT10M');
        $end = $start->add($duration);

        header('Content-Type: text/calendar; charset=utf-8');
        header('Content-Disposition: attachment; filename="My-Site-Reminder.ics"');
        $calData = array(
            'BEGIN:VCALENDAR',
            'PRODID:-//My Site//Reminder//EN',
            'VERSION:2.0',
            'BEGIN:VEVENT',
            'RRULE:FREQ=DAILY;INTERVAL=1',
            'DTSTAMP:' . $now->format('Ymd') . 'T' . $now->format('His'),
            'UID:4088E990AD89VW3DBB4849094',
            'DTSTART:' . $start->format('Ymd') . 'T' . $start->format('His'),
            'DTEND:' . $end->format('Ymd') . 'T' . $end->format('His'),
            'SUMMARY:' . $title,
            'DESCRIPTION:' . $title,
            'X-ALT-DESC;FMTTYPE=text/html:' . $title,
            'END:VEVENT',
            'END:VCALENDAR'
        );
        $calData = implode("\r\n", $calData);
        echo $calData;
        exit;
    }
}

That opens this prompt:

That is all working fine, however ideally I would like to hide the URL from the display and instead show the name of the event: 'Would you like to subscribe to [Event Name]?'

I know it must be possible to do it because they do it on https://www.addevent.com/add-to-calendar-button :

However, I have no idea how to get this to display in this way instead of showing the URL. Does anyone know?

The name of the calendar, which appears in the prompt, can be set by including...

X-WR-CALNAME:Your Custom Name

...in the body of the ics output.