Good day John,
It's seemed like you are trying to connect an on-prem based SharePoint Site.
Or the gov sites have their own domain name and you need to find the real Site URL.
If the SharePoint Sites is Hybrid or it's On-Prem site, you need to use the gateway to connect with them.(should be very hard to push)
https://learn.microsoft.com/en-us/power-apps/maker/canvas-apps/connections/connection-sharepoint-online#create-a-connection
https://learn.microsoft.com/en-us/power-apps/maker/canvas-apps/gateway-reference#use-a-gateway
If the SharePoint Sites have URL Mapping(like SharePoint Server), you need to find the real URL and try it again.