@epyles: You can't have two different passwords for the same account. I assume you mean that you have two separate accounts, in which case you should sync with the account you previously used in the Zotero app.

The account you're posting from has never been used for syncing, but it does have a storage subscription and belongs to a group. If you want us to transfer the storage subscription to your syncing account, email us at storage@zotero.org with details. You can join the same group from the other account.

If you sync with the account you're posting from, it'll wipe out your local data, as it's warning you, so don't do that.