reminders unavailable the owner stopped sharing, or you dont have permission to open it

Hi gabrielharo,

If you're having trouble sharing reminders, make sure you're following these steps:Share and assign reminders on your iPhone, iPad, or iPod touch - Apple Support

Share a list

1. Open the Reminders app. Tap the list that you want to share.

2. Tap the More button , then tap Share List.

3. Tap Share Options to choose whether the people you add can add others to the list, then choose how you'd like to invite people to the list.

4. Add the people you want to share the list with, then send the invitation.

After someone accepts your invitation, they can add items, delete items, and mark them as completed. To view shared lists that you create in iOS 13 or later, the people you invite also have to have iOS 13 or later on their device. Notifications that you set for your reminders aren't shared with anyone else.

If that's not what you need help with, reply with some additional details.