For words that only have 3 letters, there is no 4th letter. By way of example with the word “insert”, there are no far more letters Later on and so need to be the word "add". The word “addict” is inside the BIP39 wordlist however, you might have employed “addi” https://bookmarkassist.com/story18741280/the-ultimate-guide-to-bip39-seed-phrase-github