Check iCloud storage is enabled (on) for your account and your device:
iOS: go to Settings > Tap on your name > iCloud, find iReal Pro in the list of apps, turn on;
Mac: click on System Preferences > iCloud. Enable iCloud for your account.
System Prefs > iCloud Drive>Options. Find iReal Pro in the list of apps, enable.

iCloud sync will also be disabled if you have run out of  your iCloud storage.