For words that only have three letters, there is absolutely no 4th letter. For example with the word “add”, there are no additional letters afterwards and thus needs to be the word "increase". The word “addict” is during the BIP39 wordlist however, you might have used “addi” for “addict”. Acquiring https://bookmarkwuzz.com/story19017748/the-basic-principles-of-bip39-passphrase-generator