For words that only have three letters, there's no 4th letter. For example with the word “add”, there won't be any far more letters Later on and thus need to be the word "add". The word “addict” is from the BIP39 wordlist but you might have used “addi” for “addict”. https://telebookmarks.com/story10066043/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool