Please make sure you are logged into the same exact Discord account on both devices.
First, log out by going to Discord "settings" and then "log out". Once you are logged out log back in using your email address and password. Do this on all devices.
Then you can click the "Generate New Invite" link in your welcome email and it will add the server to all your devices.
If that doesn't happen it means you are logged into different Discord accounts, and you need to logout fully again and log back in with the correct email and password.
Using the "Generate New Invite" link multiple times will just kick you out of the Discord you are currently logged into. It's only intended to be used a single time.
We hope this helps, and let us know if you have any other questions!