For words that only have 3 letters, there isn't any 4th letter. One example is with the word “insert”, there won't be any extra letters Later on and thus should be the word "add". The word “addict” is in the BIP39 wordlist however , you might have applied “addi” for https://expressbookmark.com/story19021484/5-simple-techniques-for-bip39-seed-phrase