For words that have only three letters, there is absolutely no 4th letter. For instance with the word “incorporate”, there aren't any a lot more letters Later on and therefore should be the word "add". The word “addict” is in the BIP39 wordlist however , you might have employed “addi” https://bookmarkspedia.com/story4587274/an-unbiased-view-of-bip39-seed-phrase-github