When playing BABYLON'S FALL, your SQUARE ENIX account (SQEX account) will be linked one-to-one with the account of the platform you are playing on. If you create a new platform account, you will unable to use it with the SQEX account that's already linked to another platform account.
You can however link the same SQEX account to accounts from separate platforms. For example, it is possible to link a single SQEX account to one PSN account and one Steam account.
Please read
this article if you made a mistake when linking your platform account to your SQEX account.