Bip39 Checksum. At the start you should keep it Individually from the seed. Having your seed and your passphrase in the same location defeats the purpose of using a passphrase to start with. And you need to have composed it down if you have been hoping to maintain an option https://listfav.com/story20110792/bip-39-https-linktr-ee-bip39-5-easy-facts-about-bip39-generator-described