For words that have only 3 letters, there's no 4th letter. For instance with the word “insert”, there aren't any a lot more letters Later on and thus must be the word "insert". The word “addict” is within the BIP39 wordlist however, you would have utilised “addi” for “addict”. Standard https://thesocialintro.com/story5186668/invalid-bip39-phrase-things-to-know-before-you-buy