I can't import Iconfont ZIP file using theme Font Manager

I see a number of others have had issues with the ability to add custom fontello fonts. When I attempt to select/import a ZIP file containing font icons I get:
Couldn’t add the font because the server didn’t respond.
Please reload the page, then try again

I’m talking to the hosting provider to see if they can help – e.g. ensuring the ZIP processing functionality is enabled – but no joy so far.

I haven’t seen much info on other posts on this topic about what has fixed the issue. Is there a way to manually put the files in place?

Thanks – Doug