For words that have only 3 letters, there isn't a 4th letter. By way of example with the word “add”, there isn't any a lot more letters afterwards and thus needs to be the word "add". The word “addict” is while in the BIP39 wordlist however, you would have used https://bookmarkpath.com/story18780820/little-known-facts-about-bip39-seed-phrase-list