For words that have only three letters, there is absolutely no 4th letter. One example is with the word “insert”, there isn't any a lot more letters afterwards and thus should be the word "add". The word “addict” is during the BIP39 wordlist however , you might have employed “addi” https://postheaven.net/tiablexcen/mastering-your-copyright-protection-the-essential-overview-to-bip39-passphrases