Yes, that is exactly what I explained in the message immediately above yours.
Something about logging in to calendar & contacts allows Exchange AS to start functioning. My guess is that logging in this way generates a key that AS needs before it can work, but it’s only a guess.
I noticed the exact same problem yesterday. You will have to log in to Nextcloud before exchange support is available for your account. A bit tedious when having a lot of accounts.
This is a serious issue - while the suggested “logging in to NextCloud” will work for a single device, it doesn’t work if you have these accounts installed on multiple iOS devices. The moment you log into a particular device with NextCloud, the other devices get the error.
As has been established, this seems to be a z-push error (hence outside of the purview of anything @JoshData can fix), but it effectively renders the Exchange feature useless for anyone with more than one device.
My only questions here :
is the current version of MiaB using the latest version of z-push? (there has been some talking in 2017 that the more current version of z-push might have addressed this)
do we know if z-push developers are aware of this (considering it has been an issue dating back to 2014, I would assume so).