Bip39 tool https://www.sbnation.com/users/typhanhmdy Checksum generation: A checksum is produced from this entropy applying SHA-256 hashing, which helps confirm the mnemonic's integrity later. For words that only have 3 letters, there is not any 4th letter. As an example Using the word “add”, there aren't any additional letters afterwards and therefore https://digibookmarks.com/story20311002/bip39-nedir-the-smart-trick-of-bip39-wallet-that-no-one-is-discussing-https-dzen-ru-bip39-phrase-com