I cannot see my Outlook calendar on my Apple calendar

I have shared my Apple calendar to my Outlook calendar. I can see Apple calendar events on my Outlook calendar. I have tried to share my Outlook calendar with my Apple calendar. When I click the link in the sharing invitation email, I always get a Microsoft error message saying "We can't sign you in right now. Please try again later." How can I open the Apple calendar on my phone and see my Outlook events?