kourtnieriv did you get it fixed?
What I see is it looks like you're grabbing the url from where you bought it. You need to upload the font file to the squarespace css section, then put your cursor between the ' ' then click on the file you just uploaded under manage files and it will automatically paste your font url.
it should look something like this:
url('FontURLhttps://static1.squarespace.com/static/5e1ce8f116247578368a945c/t/6351b2da1df162256b217a2d/1666298586423/modernline.ttf');
The video on this page can help you: https://squaremuse.com/blog/how-to-upload-custom-fonts-squarespace