Apple’s iCloud services are crucial for Ulysses to function properly: Not only is iCloud needed for the synchronization of your groups and sheets, but it is also required for detecting and transferring your subscription across devices.
Apart from iCloud being misconfigured or disabled at all, a frequent source of error in Ulysses is a full iCloud quota. Apple offers each user 5 GB of iCloud storage for free. However, with iCloud Photos and Backup enabled (which is the default), these can fill up pretty fast.
To check how much of your iCloud quota is already used up, please follow the instructions on this website:
There, you’ll also find information on how to make more space available in iCloud. Of course, you can upgrade your iCloud storage plan anytime on the following Apple website: