For words that have only three letters, there's no 4th letter. As an example with the word “insert”, there isn't any far more letters afterwards and therefore needs to be the word "include". The word “addict” is from the BIP39 wordlist but you might have utilised “addi” for “addict”. Mnemonic https://setbookmarks.com/story19069029/bip39-seed-phrase-fundamentals-explained