For words that only have three letters, there is absolutely no 4th letter. One example is with the word “increase”, there aren't any extra letters afterwards and therefore should be the word "include". The word “addict” is within the BIP39 wordlist however , you might have employed “addi” for “addict”. https://dailybookmarkhit.com/story18867809/examine-this-report-on-bip39-passphrase