Wanted to test Backblaze and worked from mainWP but clients (sites) back failed as the credentials for BackBlaze were not transmitted to the clients/sites (like it does do with S3, for example).
Using latest mainWP and all plugins are updated to latest versions.
When I change the back in Updraft and save, it indicates it pushed the new settinsg to the sites perfectly yet when I log in to the client/site the backblaze credentials are not there (therefore upload from planned backups goes wrong).
Due to security reasons imposed by the providers of remote storage options, some of them may need to be authenticated on the child site itself.
Meaning you would need to go to the WP Admin of the child site on which you wish to use Backblaze and authorize that cloud provider in the UpdraftPlus settings.
After that initial authentication, the rest of the setup can be performed via MainWP Dashboard.