CSS Fonts on iOS

I’m trying to display font-family: ‘Montserrat’; on iOS safari. The font Montserrat-Regular.ttf is included in the project as part of the build in the fonts folder of the assets.

The CSS works fine for desktop Chrome but on iOS iPhone it just displays the default font. Any ideas why and how to fix?

I know the rest of the css section is being run correctly as I can change font colours etc and see the outcome on iOS.