For words that only have three letters, there's no 4th letter. For example with the word “insert”, there aren't any extra letters afterwards and therefore must be the word "insert". The word “addict” is inside the BIP39 wordlist however , you would have applied “addi” for “addict”. You have to https://bookmarklogin.com/story18937866/the-basic-principles-of-bip39-passphrase-generator