Please tell us your current firmware version: Settings > System > About Phone > Software information
Which version are you trying to update to?
For firmware updates for ZC600KL (CPU:630), you can check the files here:
You may also download them and update manually on your phone: https://www.asus.com/support/FAQ/1009748/
Or you may check updates in Settings> System > System updates.
Thank you 🙂