If you have ensured all of the following, and it still doesn't work, contact Apple Support:
Set up Universal Clipboard
Use Universal Clipboard with any Mac, iPhone, iPad, or iPod touch that meets the Continuity system requirements. It works when your devices are near each other and set up as follows:
- Each device is signed in to iCloud with the same Apple ID.
- Each device has Bluetooth turned on.
- Each device has Wi-Fi turned on.
- Each device has Handoff turned on:
- On Mac, choose Apple menu () > System Preferences, then click General. Select “Allow Handoff between this Mac and your iCloud devices.”
- On iPhone, iPad, or iPod touch, go to Settings > General > Handoff, then turn on Handoff.