How do I send a file_download event to google analytics?

Google Analytics considers a file download a link to one of their supported file types. But my single page app generates files on the fly and then generates a hyperlink with base64 data and prompts the user to download it. I want to capture that event as a Conversion as far as analytics is concerned. After my file download code, I’m sending

gtag('event', 'file_download', {'send-to':'downloads'}); 

I see the event being posted in the console and google reports a 204 No Content status back, so everything is working at the network level. But I am not seeing any events listed under Events > events or Engagement > events or even Dashboard > top events. What could be going wrong?