For words that only have 3 letters, there isn't any 4th letter. By way of example with the word “add”, there are no more letters Later on and thus must be the word "insert". The word “addict” is within the BIP39 wordlist however , you might have applied “addi” for https://minibookmarks.com/story18842871/the-ultimate-guide-to-bip39-seed-phrase-github