For words that have only 3 letters, there's no 4th letter. As an example with the word “include”, there are no more letters Later on and so need to be the word "insert". The word “addict” is while in the BIP39 wordlist however you might have used “addi” for “addict”. https://isocialfans.com/story4466917/invalid-bip39-phrase-things-to-know-before-you-buy