For words that have only three letters, there isn't a 4th letter. For example with the word “increase”, there isn't any additional letters Later on and therefore have to be the word "increase". The word “addict” is inside the BIP39 wordlist but you might have utilized “addi” for “addict”. By https://socialimarketing.com/story4569926/the-invalid-bip39-phrase-diaries