My friend is unable to open my reminders list and notes on his iPhone.

Hi Jacefromspace,

Thanks for reaching out to Apple Support Communities. It sounds like you're having an issue with your friend opening notes or reminders shared. We recommend passing along the following information to help.

First, we recommend ensuring they are signed into the same Apple ID account you sent the invite to. Next, on a known working connection test sending a list or note from their device to yours to see if there are any issues. The article below will help.

Share your notes on your iPhone, iPad, or iPod touch

Share notes and collaborate on iPhone

For reminders:

Share and assign reminders on iPhone

Use Reminders on your iPhone, iPad, or iPod touch

You'll also want to ensure they've upgraded the apps. Check out the section "Upgrade your iCloud reminders" section in the Set up Reminders accounts on iPhone article above.

If the issue continues have them try a normal restart of their iPhone: Restart your iPhone and check they are running the latest iOS version available for their device: Update your iPhone, iPad, or iPod touch

Cheers!