I have used 300 GB from a total 1 TB storage ipad so why does it say not enough storage?

Hello SadApple123,

Thank you for reaching out to Apple Support Communities.

They storage alert may be referring to your iCloud. If that is the case, these steps should help:

"Make more space available in iCloud

If you run out of iCloud storage, your device won’t back up to iCloud, new photos and videos won't upload to iCloud Photos, and iCloud Drive, other iCloud apps, and messages won't stay up to date across your devices. And you also won't be able to send or receive emails with your iCloud email address.

You can free up storage in iCloud by deleting content that you're not using:

• Reduce the size of your iCloud Backup
• Delete photos in iCloud Photos
• Delete folders or files in iCloud Drive
• Delete texts and attachments in Messages
• Delete messages and manage Mail
• Delete voice memos

Before you delete anything, you might want to archive or make copies of the information that you store in iCloud."

More details can be found here: Manage your iCloud storage

If the issue persists, can you provide a few more details? How much available storage do you have on iCloud? Also, how much total iCloud storage do you have?

Cheers!

Does Settings > General > iPad Storage show anything significant for ‘System Data’?