How do I accept a note invitation to collaborate with a friend

Hello Help-me-plz1 , 

Thank you for posting to the Apple Support Communities. 

First try to Restart your iPhone before accepting the invitation again. 

If the issue persists, please be sure all devices have the latest version of iOS installed. It is suggested to create a backup before installing any system updates: 

1. How to back up your iPhone, iPad, and iPod touch. 
2. Update your iPhone or iPad. 

You’ll also want to be sure that you have enough available iCloud storage to save this note: Check your iCloud storage on any device. 

If you are still unable to collaborate with the Notes app, please contact Apple Support for more help.

Cheers!