This error is caused by attempting to sync updated account information for an account/contact that has been archived in your Xero instance. Since archived contacts cannot be edited or updated, they must be restored in Xero before we can sync any updates to it.
To restore the archived account so it can be updated and clear the error in Recurly
- Go to Xero
- Click on Contacts
- Select All Contacts
- Click 'Archived' from the menu on the left side
- Locate and select the account that is archived from the list
- Click 'Restore'.
Once you have done this, the error will clear on the next sync.