For words that have only 3 letters, there isn't any 4th letter. For instance with the word “increase”, there isn't any much more letters afterwards and thus should be the word "insert". The word “addict” is in the BIP39 wordlist however , you might have employed “addi” for “addict”. Stability: https://todaybookmarks.com/story19147710/getting-my-bip39-words-to-numbers-to-work