For words that have only 3 letters, there isn't any 4th letter. For example with the word “insert”, there aren't any far more letters afterwards and so need to be the word "include". The word “addict” is in the BIP39 wordlist but you might have utilized “addi” for “addict”. Standard https://bookmark-dofollow.com/story21759643/fascination-about-invalid-bip39-phrase