Why is the URL of my iCal link not valid?

Are you getting the following error? 

The URL is not valid. It must start with http and have no initial or trailing spaces.

iCal links should be in the following formats:

Text must start with http
The base URL must end with a / character
There should be no spaces at the beginning or at the end of the text

Good example of a valid iCal

https://www.myicaldomain.com/?ical-info=ksjdlk303349893.ics