installing webfont

I am having trouble installing a paid webfont in generatepress. (by MyFonts).
I installed the font and the CSS file from the MyFontsWebfontsKit in the root of the site.

Then I put the following line in GP Hooks (wp_head)
<link rel="stylesheet" type="text/css" href="MyFontsWebfontsKit.css">

And I put this line in the custom css plugin:
body { font-family: FFMarselisWeb; }

The font shows only on the homepage. And not on the rest of the site. What did I do wrong? Please help, and save my day :) I did try al kinds of things, but nothing works until now.

With kind regards,
Marjon