The best way to test ROMs is to download them locally and then upload them to Eclipse. Open Eclipse and tap +. Tap on Upload and choose the ROM you want. Upload it, and it should work. However, if it isn’t one of the supported file game files, it likely won’t work, or the ROM itself could be corrupted – for this reason, only use reputable sources.
Second, if the game is supported, be patient – you need to wait for the splash screen to load. If the splash screen loads, but the Nintendo branding is missing or corrupt, Eclipse doesn’t support it.
Lastly, if it does work when you upload it, it is likely to be a bad URL. Check the IRL does actually download the ROM and doesn’t just show Download button. Dropbox is the best place to store your ROMS as it has official support.