For words that only have 3 letters, there's no 4th letter. Such as with the word “insert”, there won't be any a lot more letters afterwards and thus needs to be the word "insert". The word “addict” is inside the BIP39 wordlist however, you might have utilized “addi” for “addict”. https://ariabookmarks.com/story4492231/the-ultimate-guide-to-bip39-seed-phrase-github