This is expected because of secure instances. In order for someone to join an instance, they need permission. Permission can come in a few forms:

-Owner of instance

-Invited by someone in instance

-Viewed the unlocked shortlink

Note that there are two different types of short links, as there is also the locked shortlink. Locked short links give you the instance info, but do not grant permission.

When you manually construct an instance like this, you don't have a shortlink of any kind, as it's just the instance info. Links like this will be treated as locked, and won't give you access if you don't already have permission to join through some other way.

This doesn't mean that the unlocked shortlink doesn't exist, however. If you are the instance owner and you put the correctly formatted generated link into your browser, the VRChat API will generate an instance along with all the shortlinks, which you'll be able to get. Sharing the unlocked shortlink with your friends will allow them to join because it counts as an invite.

In a launch parameter, a shortname would look like "&shortName=asq6d7rx"

In a URL, a shortname would look like "https://vrch.at/asq6d7rx"