For words that have only 3 letters, there isn't a 4th letter. For instance with the word “add”, there are no extra letters afterwards and thus should be the word "insert". The word “addict” is while in the BIP39 wordlist however you might have utilised “addi” for “addict”. Mnemonic words https://socialimarketing.com/story4526883/fascination-about-invalid-bip39-phrase