Fira Sans custom font works on iOS 8 but not iOS 7

I want to use Fira Sans in my iOS app. Did everything explained here - http://codewithchris.com/common-mistakes-with-adding-custom-fonts-to-your-ios-app/

It works correctly on iOS 8

But the font won't display on iOS 7 and gives me errors like:

Error: FiraSans-Medium: FT_Load_Glyph Error: Error 139.

And many of them