The Technical Support here does not deal with Account/Billing related issues, at all, nor is there a section for such things other than the SQUARE ENIX Support Centre.

Though I guess this might be more about the technical use of the client, they might still be unable to answer.
The fellow players can answer, though, and mine would be, that make sure you enter your PlayOnline ID and PlayOnline Password under your Member Name in your Login Information Settings.

You should also enter your Square Enix ID there, and if you are using the One-Time Password, set that to 'Use'.

Now you should be asked for the SQUARE ENIX Account password when logging in (indeed the same one you log in with here). If you do not set these settings correctly, it will be asking for your PlayOnline Password, but you can not log in with it after transferring the POL Account to your SqEX Account.

If you have not transferred your POL Account yet, you would be unable to use your SqEX Account details to log in.


I hope this helps~