I purchased this awesome script to have the generator on my site so that some of my clients can submit and create their own sitemaps, like you guys do on https://www.xml-sitemaps.com/

Is there a way to do this? I set it all up and then realized it's seems it is just setup to work for the domain it is installed on. Thanks for the help!

standalone sitemap generator can be used only to create sitemap for your own website, it's not allowed to create sitemaps for 3rd party sites or provide it as a service, per license agreement: https://www.xml-sitemaps.com/license.html