Calendar issue on iPhone

Hi
I use Fantastical2 for my calendar. I have subscribed to OF reminders and all is well one my Mac. Both in Fantastical2 and in the stock Calendar app on the mac. However my iPhone calendar ( both the stock one and Fantastical2) will not sync the same reminders? It used to this before, but now suddenly it doesn’t work. Anyone have an idea whats going on?