How can I sync my Google Calendar with Apple Calendar on iPhone?

I have a calendar that I have added to my Google account but will not show up in my Apple calendar app no matter what. I have tried adding it 100 different ways and I can’t get it to show up. It’s perfect on my Google calendar app and I have tons of other Google calendars n my iOS calendar app but I can’t get this one subscription to show up.

[Re-Titled by Moderator]