I am getting an error when running my HTML5 ad through the ad validator.

The error I receive is under the ‘Zip file contents check’ heading and the stated error is ‘UNSUPPORTED_MIMETYPE’.

Nowhere on the web can I find any references to what this might mean in Googles docs. The only way I get the error to go away is by removing the custom font files from the zip file, however I need these as I’m using a custom font not hosted on Google Fonts. I have tried with multiple different font files & types for the sake of testing and still the same error. All docs suggest that you are able to upload custom font files with your ad so I’m a bit lost as to what is going wrong here.

Has anybody received this error before or found a solve?

Thanks