For words that only have three letters, there is not any 4th letter. By way of example with the word “add”, there aren't any additional letters Later on and therefore have to be the word "increase". The word “addict” is from the BIP39 wordlist however , you would've utilised “addi” https://ok-social.com/story4273522/an-unbiased-view-of-bip39-seed-phrase-github