For words that only have three letters, there is absolutely no 4th letter. As an example with the word “insert”, there aren't any additional letters afterwards and so has to be the word "increase". The word “addict” is while in the BIP39 wordlist but you might have utilized “addi” for https://social-lyft.com/story8715405/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator