For words that have only three letters, there is no 4th letter. Such as with the word “add”, there are no extra letters Later on and thus have to be the word "insert". The word “addict” is while in the BIP39 wordlist but you might have utilized “addi” for “addict”. https://bookmarkvids.com/story20098039/5-simple-techniques-for-bip39-seed-phrase