Can't connect to host

I have installed the UPS interface plugin but when I try to process an order in my cart or to checkout, the debugger tells me “UPS REQUEST FAILED: couldn’t connect to host”. I have triple checked my ID, password, access key, etc. I don’t get any error messages telling me my password or license number is bad in the debugger. Why can’t I get in to UPS? I have been through the installation documentation several times.

My website is https://www.sunshinegiftbaskets.com

https://www.ads-software.com/plugins/ups-woocommerce-shipping-method/