Hey Alan,
have you added CSS to declare the newly imported typeface for the elements you need? E.g. if you want the font to apply to body text, you can use
.normal, body, input, blockquote, dropdown-menu-widget .menu, .widget_categories .postform, .widget_archive select { font-family: 'Montserrat Light', sans-serif; }
You can insert the code either via a child theme or by using the “Style: Add Custom CSS” tab of the Theme Options panel.
Sincerely,
Andrii / Satori Studio