The "secret passphrase" is something you decide — something that you will easily remember, but no one else could guess. It is more secure if it is random words (e.g.: "tiger engine dress venezia ocean portal") but could also be a sentence (e.g.: "my crazy cat ate all of my gelato"). It is good to write the phrase you choose in a secure location where it will not be lost.

The error about "Missing Authority" always means that a requested credential was not entered correctly. In this case, you may have accidentally entered your "Posting Key" or "Active Key" into the field where "Master Password" was required. Ensure you are supplying the proper item!

The developer can provide further assistance on Discord: https://discord.gg/ZxFMBr3