Are you using one of the webinar integrations?
A shortener can work if the info is static, but sounds like you have some variables, but if it just to the event reg then that could possibly be made static as the event lookup.
You ight also check your code, looks like you are missing the trailing quotes... might make it wonky.
Please click <a href="{{my.Webinar_Link}}">here</a> for the webinar link.