
Hi.
Have you configured the Apple Push Certificate to your Miradore Online site? This is a mandatory step before iOS devices can be enrolled. I am not 100% sure if this could be cause the error you received, but maybe it is worth to check the certificate.
For further details, please see "Creating an Apple Push Certificate": https://onlinesupport.miradore.com/hc/en-us/articles/200632451
-Lassi