WHAT DOES BIP39 MEAN?

 inform your wallet how to find your coins guiding it in the tree and are explained in Bitcoin Improvement Proposals (BIP).If A different wallet does not help a derivation route that the original wallet supported, that doesn't indicate your coins are missing. It just indicates you might be not able to access them (since it would not know how to

Your wallet will deliver this phrase in your case after you make a new wallet. In case you have an existing phrase, you can input it into your wallet to re-crank out your wallet.Case (a) is beneficial if you have a mnemonic sentence which has an invalid checksum and you ought to use it using a wallet that not just checks the CS, but will also refu