I get error 507 when syncing with iCloud
Error 507 from iCloud essentially means you’ve got insufficient space in your account for more tasks. You may already have free space in iCloud, however this extra file-space is apparently not used for saving tasks in Reminders. The only way to solve this issue is to downsize your task list. If you’re attaching and syncing Photos with your tasks, you may consider unchecking that option in Sync Settings and deleting old, completed tasks from under the ’Done’ focus list.