For words that have only three letters, there isn't any 4th letter. For example with the word “insert”, there won't be any much more letters afterwards and thus needs to be the word "include". The word “addict” is within the BIP39 wordlist but you might have employed “addi” for “addict”. https://toplistar.com/story20668254/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator