iPad storage

Your internal and iCloud storage are entirely independent of each other. Subscribing to a higher tier of iCloud Storage does not change the amount of internal storage within your iPad - this being fixed for the life of the iPad.

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.

These support pages should prove to be helpful:

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

Perhaps it's referring to your iPad's internal storage in Settings>General>iPad Storage....

Regards

Giulio