What causes a Bad Mac exception?

[mpweya]

Hello!

as a user of this library I struggle with the issue of InvalidMessageException - No valid sessions. [InvalidMessageException - Bad Mac!][0] as raised in other issues as well which mostly weren't resolved (at least not with a publicposted solution).

While the library works for me in a minimal example, plugging it into my larger code base results in the aforementioned issue. To investigate how this issue occurs I would like to know, what exactly this error message means?
What causes the mac verification to fail on a WhisperMessage?

[anisalibegic]

Have you figured this out?