On very rare occasions, our magic invite link doesn't work for a user. There are essentially 2 workarounds for this:
Instead of trying to join via the link on a mobile device, have your friend click the link on a desktop browser like Google Chrome instead.
Have your friend join the app first, and then send them an invite via username. You can do this by going to your invite button on the mobile app. It will bring up a screen like this:
At the top of this screen, tap on the magnifying glass icon in the top-right corner to search all Sleeper usernames.
Once you press the invite button and confirm, an invitation will be sent to the user through the web and mobile app. This will allow them to join without that actual link.
Hope this helps!
If you tried options 1 & 2 and are still stuck, please contact [email protected]