For words that have only 3 letters, there is absolutely no 4th letter. For instance with the word “increase”, there won't be any extra letters Later on and thus has to be the word "insert". The word “addict” is from the BIP39 wordlist however, you might have utilised “addi” for https://totalbookmarking.com/story18944521/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool