1. Edit > Preferences > Quicken ID Sync & Alerts
2. Click the link to “Reset your cloud data”
If the issue persists after this step, I would save a backup file and then restore the backup. This will create a new cloud account.
To save a backup and restore a backup- see below
File > Backup and Restore > Back up Quicken file.
File > Backup and REstores > Restore from Backup file.
I would then attempt to sync once more.
Let us know if the issue persists!