I have room in iCloud storage but my iPad is full. Have already optimized

If your internal storage is full, your only option is to better manage the storage that you have - and delete unused Apps or unneeded data.  While you can subscribe to additional iCloud storage, this is not a substitute for local device storage - this being fixed for the entire life of the device.

These support pages should prove to be helpful:

About storage on your device and in iCloud – Apple Support

What's the difference between device storage and iCloud storage? – Apple Support

Manage your iCloud storage – Apple Support

How to check the storage on your iPhone, iPad and iPod touch – Apple Support

Clear Other storage on your iPhone or iPad - Apple Support

What's the point of "Optimize this Mac" if iCloud Drive still lets your local drive get full?