Your webcal link isn't working
webcal:// is not a protocol of its own; it is an https URL wearing a different scheme so your operating system hands it to a calendar app instead of downloading it. When a webcal link does nothing, the OS has no app claiming the scheme, and when it errors, the URL underneath is usually the problem. Swap webcal:// for https:// in the address and you can test the feed directly.
Work through these, most likely first
1Nothing is registered to handle webcal://
On Windows especially, no default app may claim webcal links, so clicks silently die. Add the calendar by URL from inside your calendar app instead: Outlook and Google both have an 'add from URL / subscribe' option that takes the https form of the same link.
2The underlying URL is broken
Replace webcal:// with https:// and open it in a browser. If you don't get a file full of BEGIN:VEVENT lines, the feed itself is dead or the link got truncated in an email or text message.
3Chat apps and email clients mangle long links
Long feed URLs get cut at line breaks or wrapped by link scanners. Copy the link with a dedicated copy button where offered, and compare the pasted URL's ending with the original.
4The link opens the wrong calendar account
On a phone with several calendar apps, the webcal handler may not be the app you expect. Subscribe from inside the app you actually use rather than tapping the link.
Rarer, but worth knowing
Corporate networks. Some proxies block unusual schemes outright. The https form added from inside the calendar app goes through normal web traffic and usually survives.
TangoHive share pages put the feed behind clearly labeled Apple / Google / ICS buttons, each using the form that platform actually accepts, so nobody has to know what webcal means.