JS icon should be 48x48px (or slightly under) but is instead 0x0px

Grateful for any help here. I'm getting the following error building an app, wondering if there's a common cause of it:

JS icon geminiclock.img should be 48x48px (or slightly under) but is instead 0x0px

My source icon is 48x48 pixels and I think I used all the suggested settings for conversion, and indeed tried many others, but the build always fails the same way. A typo or error in the JSON file seems likely but I can't spot it. Code is here: https://github.com/blogmywiki/BangleApps/tree/master/apps/geminiclock

Update - I've now got the app to build by pasting in the code for another app's icon into the app-icon.js file, but oddly the app has the intended new icon when uploaded to my watch, not the icon of the app I copied the code from. So I'm very confused as to what role the encoded app-icon.js file plays - I thought it determined the app icon as it appears on the watch but it seems not?

I'd be grateful if someone with a BangleJS2 could try uploading my geminiclock app from here and let me know if the app icon in your watch menu appears as a number 11 (icon from another app as placed in the app-icon.js file) or, as it appears on my watch, the number 23 (icon in the app.png file): https://blogmywiki.github.io/BangleApps/?q=gemini

Sorry, I missed this when you posted it...

I see 23 on mine...

Maybe you were doing 'image object' in the image converter and copying out just the 'buffer' part, when actually you should do 'image string' and copy everything?