In general you want to set the default domain, and that’s generally the www version. To do that, click Make default next to the www name, and republish.
That will ensure that the sitemap correctly generates entries like https://www.gptforhr.com/contact rather than https://gptforhr.com/contact ( no www ).
When you do not set a default domain, Webflow sort of randomly picks one of your domains as the one to use in the sitemap.xml.
If you’ve already set a default domain, and republished, then you might be manually generating your sitemap.xml - in that case you need to update it manually to include the www to avoid that redirect.