Well, as you are attempting to play the game on an account that does not own a license for the game, it will not work... Licenses do not transfer between platforms, and Battle.net does not offer game sharing. As your linked Battle.net account does not own the game, you will not be able to play on that account. You must own the game, and any DLC that you wish to play, on each platform account that you wish to play on. You’ll need to deactivate cross-save, to unlink the incorrect account and link up the correct one, which will incur a 90 day cooldown period for reactivation. Or you’ll have to wait for Shadowkeep, and just utilize Steam, but you’ll lose your previous Forsaken license, as it was not properly linked for migration. So you’ll have to decide which you’d rather deal with; a 90 day wait, or having to possibly buy content again.
Have you read the help topic [url=https://www.bungie.net/en/Help/Article/46139]Here[/url]?