Backup to mega.nz doesn’t seem to work. No files are created at the remote location.
When I looked at the frontend of duplicati, everything seems to be fine.
Mega.nz error when check connection talks about a problem with new mega accounts having changes which make them incompatible with Duplicati. They have no published API and don’t like third-party services, but the library that Duplicati uses was updated and will be in the next beta. Are you currently on some Duplicati Beta?
Using 2.0.4.23_beta_2019-07-14. I do not get any error messages.