For words that have only three letters, there is absolutely no 4th letter. One example is with the word “increase”, there isn't any more letters afterwards and therefore should be the word "include". The word “addict” is from the BIP39 wordlist however you might have employed “addi” for “addict”. The https://ezmarkbookmarks.com/story18925928/the-ultimate-guide-to-bip39-seed-phrase-github