hard_riceprobably meant CD-key hash. Your personal CD-key is much more sensitive information and you should not share it with anyone.
If you banned from the server, you can ask any admin to look in ban list, and provide our staff with your CD-key hash instead through PM.
To get your hash you can use, for example, this program: https://www.moddb.com/downloads/bf-easy-key-hasher
But first, have you tried to re-register your CD-key? Your CD-key registration settings may be off for some reason, so you might want to register it again.
Try to open this file: Your Battlefield Vietnam folder\eReg\Battlefield Vietnam_code.exe
and insert your CD-key again and then click "Next>" button.
I've never got banned , because I never joined any server, this is my first attempt to join an online server
I don't know where to insert the cd key,since the installation didn't require any cd key,should I try other download? ( I didn't bought the original BFV , just downloaded , could that also interfer?)
Edit: I found Battlefield Vietnam_code, but it doesn't contain any CD key so since I download the game from [Omitted by Moderator] , I decided to download the 2 version which is the full game , and contains Cd keys, I can link those if you want
Currently we have only one, the largest BFV server out there, which you can find on our main page: https://www.helloclan.eu/pages/bfv/
It's online 24/7, but players are mostly gathering closer to the evening/night times.
If you have this error again, you can always go to your game folder and insert your cd-key in Battlefield Vietnam_code.exe again.