NOTE: THIS ARTICLE IS ONLY RELEVANT FOR USERS WHO HAVE NOT BEEN MIGRATED IN CONSOLE.
Learn more about the migration here.
Check if you have been migrated here.
It’s important to note that sandbox and live applications are separate applications - and as such require the admin to invite them to join the application once from the sandbox, and once in the live environment if they’re trying to give access to both parts.
This is intentional, as often a different set of members are required for sandbox and live environments.