For words that only have 3 letters, there is absolutely no 4th letter. By way of example with the word “insert”, there isn't any far more letters afterwards and so need to be the word "incorporate". The word “addict” is from the BIP39 wordlist however you would've utilised “addi” for https://linkingbookmark.com/story18700226/bip39-seed-phrase-fundamentals-explained