My iPad is not synching my calendar from my iPhone

Start here:

If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support

Assuming that both devices are signed-in to iCloud with the same AppleID, ensure that Calendars for iCloud has been enabled for both your iPhone and iPad:

Settings > [Your Name / AppleID] > iCloud > Calendars - set to ON

If you continue to have difficulties, try disabling Calendar for iCloud on each device - and when prompted, accept to option to “save a local copy” of your Calendars on the respective device. Then perform a forced-restart of both iPad and iPhone:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

After restarting, re-enable Calendars in iCloud on both devices.

If difficulties persist, you may need to seek assistance directly from from Apple Support. You can contact the Support Team using the Get Support link at top-right of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044