For words that only have three letters, there is no 4th letter. One example is with the word “insert”, there are no a lot more letters Later on and thus must be the word "increase". The word “addict” is during the BIP39 wordlist however, you might have applied “addi” for https://bookmarkize.com/story19050644/invalid-bip39-phrase-things-to-know-before-you-buy