Building on what everyone has said above, it's not compulsory to fill in the OTP space while logging in to the forum. It's an optional layer of security that was initiated to protect people's accounts as it's a personal one time password that requires only the original owner of the account to fill in hence it reduces the rate of hacks and all sorts of security compromised in the forum.
The link @Crypto Library dropped above will guide you on how to enable it, then you can begin to use that option during your login time if necessary.
And I think this topic should be on Meta Board
I think it's okay here afterall this board is open for any thing that is related to help, except it seems necessary to be moved hence I believe here is okay.