For words that have only three letters, there's no 4th letter. As an example with the word “increase”, there are no more letters Later on and so need to be the word "insert". The word “addict” is from the BIP39 wordlist however you might have used “addi” for “addict”. Meticulously https://bookmark-group.com/story4483864/the-ultimate-guide-to-bip39-seed-phrase-github