Invalid URL error on local .dev site

While uploading images to a local install with a .dev domain, ShortPixel gives me an error: There was an error and your request was not processed. (Invalid URL. Please make sure the URL is properly urlencoded and points to a valid image file.)

I’m impressed to have received an email from ShortPixel informing me that my URLs “were not accessible to our optimization servers.” The email suggests an IP Whitelisting solution under the assumption that I have some kind of firewall up. But I don’t and I suspect it’s the .dev that’s uncooperative instead?

Thanks so much.